Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83

Contents lists available at SciVerse ScienceDirect

Palaeogeography, Palaeoclimatology, Palaeoecology

journal homepage: www.elsevier.com/locate/palaeo

Preservation of exceptional vertebrate assemblages in Middle Permian fluviolacustrine mudstones of Kotel'nich, Russia: stratigraphy, sedimentology, and taphonomy

Michael J. Benton a,⁎, Andrew J. Newell b, Al'bert Yu. Khlyupin c, Il'ya S. Shumov c, Gregory D. Price d, Andrey A. Kurkin e a School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK b British Geological Survey, Maclean Building, Wallingford OX10 8BB, UK c Vyatka Palaeontological Museum, Ulitsa Drelevskii 22, Kirov, Kirov Region 610000, Russia d School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK e Paleontological Institute, Russian Academy of Sciences, Ulitsa Profsoyuznaya 123, Moscow 117997, Russia article info abstract

Article history: The Kotel'nich locality in European Russia has long been a rich source of high-quality tetrapod fossils, including Received 2 July 2011 pareiasaurs, dicynodonts, gorgonopsians and theriodonts. The age of the Kotel'nich locality has been debated, but Received in revised form 13 December 2011 it corresponds to early Severodvinian in the Russian stratigraphic scheme, equivalent to the late Capitanian (late Accepted 2 January 2012 Middle Permian) on the international time scale. Remarkably, the majority of specimens are complete, quite un- Available online 8 January 2012 like those from most Russian Permo-Triassic red bed localities; commonest of all are 1–2-metre long pareia- saur skeletons of the genus Deltavjatia, preserved in hollows on top of a consolidated palaeosol horizon. Keywords: Taphonomy Previous taphonomic scenarios in the Russian literature have included suggestions that the animals were Tetrapod skeleton overwhelmed beneath sand dunes, mired in soft fluviatile sediments, caught at the bottom of a deep lake, Drought trapped in burrows, or dumped in fluviatile scours. It is probable that the pareiasaurs were searching for Fluvial scour water in a time of catastrophic aridification, and died, weakened, in shallow hollows. In this case, we also em- Permian phasise the importance of floodplain microtopography in creating the sedimentary conditions necessary for the Russia preservation of exceptional vertebrate assemblages in a slowly aggrading fluviolacustrine setting. Severodvinian © 2012 Elsevier B.V. All rights reserved. Vyatkian

1. Introduction of the enclosed vertebrate fossils. This uncertainty is exemplified by the renowned Permian vertebrate locality of Kotel'nich in Russia. Vertebrate skeletons in ancient river deposits are commonly pre- Kotel'nich has yielded hundreds of complete skeletons of fossil served as lags within coarse-grained channel deposits where the re- reptiles, predominantly pareiasaurs and dicynodonts. The mode of mains have generally been transported, disarticulated and abraded. preservation of these skeletons has been debated (Hartmann- Less common, but often of greater paleontological importance, are Weinberg, 1933, 1937; Kashtanov, 1934; Ivakhnenko, 1987; Gubin, skeletons preserved within fine-grained floodplain deposits that are 1989; Tverdokhlebov and Shminke, 1990; Ochev, 1995; Khlyupin, often substantially complete and well preserved (Behrensmeyer, 2007; Sumin, 2009; Tverdokhlebov, 2009): were they preserved by 1988; Smith, 1993; Rogers and Kidwell, 2000; Therrien and miring in soft muds around water holes, deposited on the floor of a Fastovsky, 2000; Ryan et al., 2001; Smith and Swart, 2002; Straight lake, buried in situ within burrows, or washed into floodplain hol- and Eberth, 2002; Rogers, 2005; Eberth et al., 2007, 2010; González lows? Further, although the Kotel'nich locality has been known Riga and Astini, 2007). In comparison to coarse-grained channel de- since the 1930s, and it has been referred to hundreds of times in posits, floodplain mudstones often have a relatively uniform stratig- the vertebrate palaeontological literature, the geology and taphono- raphy that can be masked by syndepositional soil-forming processes my of the site have not been described. The aims of this paper are and this can lead to uncertainty regarding the original depositional (1) to outline the stratigraphy and sedimentology of the Middle environment of the muds as well as the life, death and preservation Permian continental red beds on the banks of the Vyatka River at Kotel'nich, which requires a presentation of the local stratigraphic scheme as well as new evidence for the dating of Kotel'nich in com- parison to the Karoo tetrapod biozones and the international marine ⁎ Corresponding author. Tel.: +44 954 5400; fax: +44 925 3385. time scale, and (2) to describe the taphonomy of recently excavated E-mail address: [email protected] (M.J. Benton). tetrapod skeletons, and to present evidence that the exceptional

0031-0182/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2012.01.005 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 59 preservation of the fauna results largely from an arid episode and the Agafonovo (58.18637N, 48.32864E). The spectacular red, yellow, rapid infill of floodplain hollows. and brown colours of the near horizontally-bedded clastic sediments Museum abbreviations. KPM, Vyatka Palaeontological Museum, have been noted by previous authors (Fig. 4). Kirov, Kirov Oblast, Russia; PIN, Paleontological Institute, Russian Geological work on the Kotel'nich red beds began rather late, with Academy of Sciences, Moscow, Russia. the first geological mapping only 100 years ago (Krotov, 1912). This was because the area was remote from major cities, and seemingly 2. Geological background devoid of mineral potential. The Vyatka River had long been a major transport artery, but the town of Kotel'nich remained a very remote The Permo-Triassic red beds of Russia represent an enormous area outpost of the Russian Empire until the railway from St Petersburg of outcrop, covering 1.4×106 km2 of European Russia (Fig. 1), and to Vyatka opened in 1905. Following continued repression during spanning over 40 million years, from the end of the Early Permian Soviet times, and substantial decline of industry after 1990, Kotel'nich (Ufimian; Kungurian) to the end of the Middle Triassic (Bukobay; remains a remote and undeveloped town. The geology of the Permian Ladinian). These units provide an important record of changing terres- red beds was revised by Ignat'ev (1962, 1963) and Tikhvinskaya trial environments and ecosystems before, during, and after the end- (1946),andreviewedbyNalivkin (1973) and Lozovskiy and Esaulova Permian mass extinction, including long-term aridification of climates (1998). In these works, the sedimentary rocks were interpreted as flu- and major changes in sedimentary regimes across the Permo-Triassic viatile and lacustrine. Tverdokhlebov and Shminke (1990) were the boundary (Newell et al., 1999, 2010; Golubev, 2000; Zharkov and first to argue that the yellow sandstones of the Boroviki Member Chumakov, 2001; Tverdokhlebov et al., 2003, 2005; Benton et al., (Coffa, 1999) were aeolian in origin. Then, Goman'kov (1997), Coffa 2004; Shishkin et al., 2006; Shcherbakov, 2008; Krassilov and Karasev, (1999),andGolubev (2000) presented summary accounts of the sedi- 2009; Benton, 2012). mentology and stratigraphy of the Kotel'nich succession, each based One of the most remarkable localities in the Russian Middle and on original and independent fieldwork, and Tverdokhlebov (2009) Late Permian is Kotel'nich, in Kirov Oblast, the source of hundreds added further first-hand observations. of tetrapod specimens since their first discovery in 1893. In his semi- The Kotel'nich red beds are renowned for their abundant and nal work on the stratigraphy of the Russian Permian tetrapods, exquisite tetrapod fossils, and yet earlier geologists did not pay these Efremov (1937, 1941) established two lower, dinocephalian, com- much attention (see Ochev, 1995; Ochev and Surkov, 2000 for historical plexes (I and II), and a third, pareiasaurian, complex (III) based initial- surveys). Krotov (1894, 1912) recorded isolated bones from the west ly on finds from Kotel'nich and Sokolki, a site on the North Dvina bank of the Vyatka River just south of Kotel'nich, at a locality later River. The pareiasaurian complex was subsequently divided into termed ‘Kotel'nich-1’. In 1933, S. G. Kashtanov, a young hydrogeologist three, the Kotel'nich, Ilinsko'ye, and Sokolki subcomplexes, occupying from Kazan' University, discovered two complete pareiasaur skeletons the bulk of the Tatarian Russian Stage (details in Golubev, 2000). near the village of Vanyushonki, on the river bank 18 km south of Kotel'nich was then one of the fundamental locations for understand- Kotel'nich (Figs. 2, 3), and he found a further two or three in 1935, ing the evolution of Middle and Late Permian tetrapods from the ear- 2 km upstream (Kashtanov, 1934). The skeletons were incomplete as liest days of palaeontological work in Russia, and it was seen they had been partially eroded by the action of the Vyatka River, but internationally as the equal and equivalent of the succession of tetra- Kashtanov excavated some of this material and sent it to the Paleonto- pod zones in the Karoo Basin in South Africa (e.g. Olson, 1962; logical Institute (PIN) in Moscow. The Moscow palaeontologists came to Anderson and Cruickshank, 1978; Benton, 1983; Modesto and Kotel'nich, beginning with expeditions led by A. P. Hartmann-Weinberg Rybczynski, 2000; Lucas, 2004, 2006). in 1935, and they found two incomplete skeletons and two skulls of Kotel'nich occupies a central position within the broad belt of pareiasaurs near the village of Volki (Fig. 3). In 1948, a team from PIN Permian deposits on the Russian platform west of the Ural Mountains led by B. P. V'yushkov, found four pareiasaur skeletons, three of them (Fig. 1), a north–south trending fold and thrust belt formed by the damaged by erosion, near Boroviki village (Figs. 2, 3). The following collision of the East European Platform and Siberian plate during the year, the same team prospected 12 km of the banks of the Vyatka Carboniferous and Permian (Nikishin et al., 1996). On the Russian River, from Port Kotel'nich south to Boroviki, and they discovered a platform, Permian strata younger than the Roadian are predominant- further seven complete and six incomplete skeletons. Two further ly siliciclastic terrestrial deposits that were largely derived from the skeletons were reported in 1950 from Boroviki village by D. M. Ural Mountains and deposited in a range of fluvial and lacustrine en- Vologzhanin, but he could not extract them. In their overview of vironments across the platform (Ignat'ev, 1962, 1963; Gorsky et al., the Russian Permo-Triassic tetrapods, Efremov and V'yushkov 2003). Proximal to the Ural Mountains, in areas such as Perm', post- (1955) reported 15 pareiasaur skeletons collected by PIN scientists Roadian continental deposits are up to 1400 m thick and contain at Kotel'nich. much cross-bedded pebbly sandstone and conglomeratic channel Renewed investigations by PIN scientists Yu. M. Gubin, M. F. fills derived from the orogen, while in distal (western) locations Mid- Ivakhnenko, and N. N. Kalandadze turned up isolated pareiasaur and dle and Upper Permian deposits are generally much thinner and therapsid specimens in several green sandstone lenses higher in the dominated by mudstones and evaporites deposited in fluviolacustrine section, in what is now termed the Sokol'ya Gora Member near Aga- environments (Gorsky et al., 2003; Newell et al., 2010). Kotel'nich fonovo (Fig. 3), a locality they termed Kotel'nich-2. Further excavations occupies a medial position within this westward thinning and fining began in the 1990s, thanks to the work of D. L. Sumin from Moscow, clastic wedge. who collected many tetrapod skeletons, including dicynodonts, droma- saurs, therocephalians, and gorgonopsians, as well as pareiasaurs. He 3. Historical context of the Kotel'nich red beds and their fauna established a fossil-dealing company called Kamyennii Tsvyetok (=‘Stone Flower’) that sold some of the fossils, but the company was Upper Permian red beds, comprising mudstones, siltstones, marls, dissolved in 1995. In the three years from 1990 to 1992, Sumin and col- sandstones, and conglomerates, are exposed on the right-hand leagues collected 40 pareiasaur skeletons on the banks of the Vyatka, (western) bank of the Vyatka River at, and for some 24 km south near the villages of Boroviki and Mukha (Figs. 2, 3). Since 1992, the of, the town of Kotel'nich (Fig. 2), from Port Kotel'nich (58.29136N, work has been led by Al'bert Yu. Khlyupin, in conjunction with teams 48.33060E) to Zemtsy (58.13931N, 48.36058E). Here the Vyatka of locally based geologists, school children, and visitors from overseas River cuts westwards into an elevated escarpment of Permian rocks (Fig. 5). These teams excavated both at Port Kotel'nich, where they creating a discontinuous series of large outcrops in the generally found many dicynodont skeletons as well as rarer pareiasaurs, and flat-lying Permian succession (Fig. 3), ranging up to 40 m high at along the southern portion of the section on the banks of the Vyatka 60 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83

Fig. 1. Map showing the location of Kotel'nich 400 km NE of Moscow in the Russian Federation. Kotel'nich occupies a central position within the broad belt of Permian strata that was deposited on the Russian platform west of the Ural Mountains. It is located just to the south of the Moscow Syncline which contains a core of Triassic and younger strata.

where they excavated many pareiasaurs and the extraordinary small The fauna has always been recognised as stratigraphically signifi- climbing reptile Suminia. Khlyupin established a museum in Kotel'nich cant. Ivakhnenko (1987, 1992) established the ‘Kotel'nich Subcomplex' in 1994, and it has since been designated as a regional museum, the (Kotel'nichskii Subkompleks) as the lowest of three faunal assemblages Vyatka Palaeontological Museum. Since 1992, the Museum group has within the Sokolki Complex that spanned the Severodvinian and lower excavated and documented over 390 tetrapod skeletons. Vyatkian gorizonts, as part of the traditional tetrapod-based division of the Russian Permo-Triassic red beds (Fig. 5; Efremov, 1939, 1941; Lucas, 4. Kotel'nich fauna and flora 2004, 2006).

4.1. Tetrapod fauna 4.2. Flora and non-tetrapod fauna The fossil amphibians and reptiles from the main Kotel'nich section are well known, including the plant-eating pareiasaur Deltavjatia The Kotel'nich red beds have produced plant fossils in addition (Hartmann-Weinberg, 1937; V'yushkov, 1953; Ivakhnenko, 1987; Lee, to the famous tetrapods. V'yushkov (1953) and Ignat'ev (1963) 2000; Kordikova and Khlyupin, 2001) the galeopid anomodont Suminia mentioned the occurrence of plants, and Goman'kov (1997) provided (Ivakhnenko, 1994; Rybczinski, 2000; Fröbisch and Reisz, 2009), and a detailed study, reporting a detrital macroplant assemblage from the the gorgonopsian Viatkogorgon (Tatarinov, 2004a), as well as the small Chizhi Member channels referable to the Tatarina flora, with the coni- insect-eating parareptile Emeroleter (Ivakhnenko, 1997), and small car- fers Phylladoderma and Geinitzia, the peltaspermalian pteridosperms nivorous theriodonts (Tatarinov, 1968, 1995a, b, 1997, 1999a, b, 2000, (seed ferns) Tatarina, Pursongia,andPermotheca, and the horsetails 2004a, b). The dicynodont Australobarbarus (Kurkin, 2000) and two par- Paracalamites and Phyllotheca, as well as miospores of the same plants eiasaurs found in 2009, possibly also Deltavjatia,comefromtheseparate that may be used in biostratigraphy. Port Kotel'nich locality. Further, the fish-eating chroniosuchian Chronio- These same organic-rich sandstone units of the Chizhi Member saurus (Golubev, 1998, 2000), the basal biarmosuchian Proburnetia have produced further fossils, including ostracod tests, fish scales, (Tatarinov, 1968), and the pareiasaur Proelginia permiana (=Scutosaurus and isolated tetrapod bones (Tverdokhlebov and Shminke, 1990; karpinskii) are known from the younger Sokol'ya Gora locality. Goman'kov, 1997; see below). M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 61

Fig. 2. Map of the Kotel'nich area showing the relatively straight, south-flowing reach of the Vyatka River to the south of the town. Permian strata are exposed on the elevated escarpment along the western bank of the Vyatka River, with most of the vertebrate localities close to the village Boroviki. Numbers with white markers show the locations of logged sections in Fig. 4.

5. Stratigraphy whole sequence was simply referred to as the ‘Kotel'nich red beds’, or an equivalent term, even though distinct horizons of red mud- 5.1. Nomenclature and correlation stone, conglomerates, and channels of green-brown sandstone had been noted. In traditional style, each fossiliferous locality was We distinguish three portions of the Kotel'nich succession, each named, Port Kotel'nich being termed Kotel'nich-1, and this term with different tetrapod faunas and different modes of preservation, was then extended to many other distinct sites in the southern sec- and each of which has to be related to the other appropriately in tion, but still in red mudstones and siltstones. The southernmost lo- order to establish the succession. From north to south (Figs. 2, 3), cality, called sometimes Agafonovo or Sokol'ya Gora, was termed these are (1) the Port Kotel'nich locality (58.29136N, 48.33060E), Kotel'nich-2. This second location is well constrained both geograph- (2) the long southern succession from Shestakovy (58.2452N, ically and stratigraphically, but Kotel'nich-1 is not, extending over 48.3179E) to Zemtsy (58.13931N, 48.36058E) with a conformable se- 20 km along the banks of the Vyatka River, and encompassing up to quence of the Vanyushonki to Shestakovy members (Fig. 3), and (3) four distinct stratigraphic levels. Coffa (1999) noted a published ex- the Sokol'ya Gora Member at Agafonovo (58.18637N, 48.32864E). ample of how the terminology became confused when Tatarinov The relationships of the last two are straightforward: the Sokol'ya (1995a, b) stated that the holotype specimens of the theriodonts Viat- Gora Member follows directly above the Shestakovy Member. The kosuchus and Karenites both came from Kotel'nich-2, when in fact Port Kotel'nich section is harder to correlate to the other two (see they came from the older Kotel'nich-1 horizon. The traditional habit Section 6.7). among Russian geologists and palaeontologists of naming locations, In addition to the geographic separation of portions of the but not horizons, often led to confusions of this kind. Kotel'nich section, there has been some confusion over the nomencla- Ochev (1995) distinguished three layers, clearly visible along the ture of these localities and the stratigraphic divisions. In general, the banks of the Vyatka River (Fig. 3): at the base a unit of reddish- 62 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83

NORTH

Sokol’ya Gora Shestakovy Vanyushonki Boroviki Agafonovo Kuznetsy Zemtsy Mukha Volki 40 30 20 10 m 0.2 km 2.2 km 1.5 km (0.5 km) 0.5 km (1.5 km) (0.5 km) 0.2 km (3.5 km) incised palaeosol and pareiasaur horizon Vyatka River Sokol’ya Gora Member - fluvial sandstone and conglomerate Chizhi Member - fluvial sandstone Shestakovy Member - fluvio-lacustrine mudstones Boroviki Member - aeolian sandstone Vanyushonki Member - fluvio-lacustrine mudstones

Fig. 3. Sketch section along the western bank of the Vyatka River between Zemtsy in the south and Kuznetsy in the north (see Fig. 2 for locations) showing the arrangement of the main stratigraphical units. The Vanyushonki Member is predominantly fluviolacustrine mudstone, which is overlain by the Boroviki Member, a flat-based, lensoid, predominantly aeolian sandbody, and the Shestakovy Member, a further series of fluviolacustrine mudstones. These are followed by the channel forms of the Chizhi and Sokol'ya Gora members, which comprise coarse-grained fluvial sandstones and intraclast conglomerates in lenticular bodies spectacularly incised into the older units. Vertebrates are primarily found in mudstones toward the base of the cliff in the Vanyusonki Member, in the marked palaeosol horizon. Distances (km) in brackets indicate breaks in exposure that are not shown in the diagram. Figure is adapted from Tverdokhlebov (2009).

brown siltstone with thin interbeds of shelly mudstone, bluish silt- stone, calcareous mudstone, and detrital sand; above this a 15–18 m thick, kilometre-scale lens of reddish and yellowish fine-grained ar- gillaceous, cross-bedded sandstones; and an upper unit, some 10 m thick, of brown and brownish-red sandy mudstone interbedded with greenish- and brownish-grey sandstone. Ochev (1995) also used the Kotel'nich-1 and Kotel'nich-2 terminology, but did not name the units within the succession he described. Coffa (1999) was the first to divide the Kotel'nich red beds formally, and he named five stratigraphic members. These are, from the base of the succession, the Vanyushonki, Boroviki, Shestakovy, Chizhi, and Sokol'ya Gora members (Fig. 3). Andre Coffa worked with Russian geologists and palaeontologists in the mid-1990s for his Masters and PhD theses at Monash University, Australia, as part of a wider Russian–Australian collaboration, but his work was published only as two conference abstracts (Coffa, 1997, 1998) and as a summary paper in a conference fieldtrip volume (Coffa, 1999). The latter is the key reference and source of the nomenclature we use here. Coffa (1999) states that his stratigraphic scheme was agreed with key Russian stratigraphers at the time, and indeed was used by Kordikova and Khlyupin (2001). Further, his scheme was in use when we did our fieldwork in 2009: accordingly, we adopt Coffa's stratigraphic terminology here. Further stratigraphic work was done on the Kotel'nich section by Goman'kov (1997), Golubev (2000),andTverdokhlebov (2009),and they supplied three different informal numbering schemes for the succession. Coffa's (1999) five members correspond, in sequence from bottom to top, to Goman'kov's (1997) beds 1, 2, 3+4, 5, and 6, and Golubev's (2000, pp. 84–88, 117–120) beds 1+2, 3+4, 6, 5, and 7+ 8. Tverdokhlebov (2009) identified four sedimentary ‘packets’,num- bered I, II, III, and IV from the bottom, and corresponding respectively to the Vanyushonki, Boroviki, Shestakovy, and Sokol'ya Gora members. Goman'kov (1997), Coffa (1999), and Golubev (2000) differ in

Fig. 4. Two views of the Kotel'nich tetrapod localities. (A) The right (west) bank of the some details of their interpretation of the Kotel'nich succession, Vyatka River, 15 km south of Kotel'nich town, near Boroviki village, at about 58.16092N, Coffa measuring a composite section of 65 m in all, and Golubev 48.34928E, showing a typical section through the red sediments of the Vanyushonki only 35 m. This discrepancy arises from differences in measurements Member on the foreshore and in the lower one-third of the cliff, a thin strip of the of the five constituent units, but partly in the placement of the Port overlying Boroviki Member sandstones, and the red sediments of the Shestakovy Kotel'nich section (see Section 6.7). We prefer to refer to the main Member above. (B) The steep-sided cliff at Port Kotel'nich (58.29136, 48.32449), close to the ‘dicynodont quarry’, excavated in the early 1990s. Photographs by Al'bert section at Kotel'nich as 35 m thick, and make no assumptions about Yu. Khlyupin. how much of the Port Kotel'nich succession might sit on top. M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 63

not identical, but merely close relatives, and so any matching can be based only on broad assumptions about phylogeny; and second, the South African succession is not yet securely dated to the international marine standard, so establishing a correlation with an approximate tetrapod biozone in the Karoo is a distraction, and it does not help in establishing the actual age of the Russian units. It will be better to seek auxiliary evidence to date the Russian and Karoo successions, such as marine intercalations, magnetostratigraphy, and radiometric dates (Newell et al., 2010; Benton, 2012), and then to use the verte- brate biozones (e.g. Lucas, 2004, 2006) to cross-match between the two successions. There are two steps in the dating procedure: first, the Kotel'nich succession has to be placed in the context of the Russian system, and then this must be equated with the international marine stan- dard by the use of biostratigraphy, magnetostratigraphy, and other evidence. Evidence for dating the Kotel'nich succession within the Russian system comes from comparative biostratigraphic studies and match- ing with sections that have also yielded magnetostratigraphic evi- dence (see Appendix 1; Fig. 6). In summary, the whole Kotel'nich succession is Severodvinian (middle Tatarian), belonging to the Suchonellina futschiki ostracod zone (Molostovskaya in Tverdokhlebov and Shminke, 1990), equivalent to the Suchonellina inornata ostracod zones (Fig. 6). The sequence spans the Deltavjatia vjatkensis tetrapod zone and the Chroniosaurus dongusensis subzone of the Proelginia permiana tetrapod zone, the Amblypterina costata and Amblypterina pectinata ichthyozones (=Toyemia tverdokhlebovi– Mutovinia stella Ichthyozone; Fig. 6; Esin, 1995; Esin and Mashin, 1998), and the PK 5 palynocomplex (Golubev, 2000, p. 123). The Vanyushonki, Boroviki, and Chizhi members (Golubev's beds 1–5) in the Kotel'nich succession were said to be equivalent in age to the Nyuksenitskaya, Mikulinskaya, and lower Strelenskaya packets, the Shestakovy Member (Golubev's bed 6) to the upper Strelenskaya, Isadskaya, and Purtovinskaya packets, and the Sokol'ya Gora Member (Golubev's beds 7 and 8) to the upper Purtovinskaya and lower Kichugskaya packets (Golubev, 2000, pp. 118–120). Having broadly established the placement of the Kotel'nich fossil- iferous beds in the Russian system, this must now be linked to the in- ternational stratigraphic standard. Hitherto, this has been achieved through magnetostratigraphy (Khramov et al., 2006; Taylor et al., 2009), comparison with red bed palynomorphs, ostracods, fishes, and tetrapods, and importantly by comparisons of marine fossils (e.g. ammonoids, brachiopods) in intercalated beds of Early and Mid- dle Permian age (full details in Newell et al., 2010). Fig. 5. Excavating pareiasaur skeletons from the Vanyushonki Member. (A, B) Scenes from the river-based 1992 joint paleontological expedition of “Stone Flower Company” The magnetostratigraphic scheme for the Upper Permian red beds of (Moscow) and Moscow Paleontological Institute, using a fire-fighting barge equipped Russia is well established (Khramov, 1963; Molostovskiy et al., 1979; with a high-pressure hose (A) to blast sediment from the low-lying palaeosol horizons to Molostovskiy, 1983, 2005), and it has recently been revised and expose pareiasaur skeletons, and then heavy lifting gear to remove the crated specimens matched to the international standard (Khramov et al., 2006; Taylor to a small river vessel (B), for transportation up the Vyatka River to Port Kotel'nich, where they were loaded onto rail wagons for transport to the Paleontological Museum in et al., 2009). Unfortunately, the Kotel'nich section is characterised by Moscow. (C) Palaeontological expedition of the Kotel'nich Palaeontological Museum in reverse magnetisation throughout (Burov et al., 1996), and there are 2006: from left to right, Maxim Kovalyov, Alexey Toropov, and Il'ya Shumov remove no long measured sections with corrected magnetostratigraphic data sediment from a complete pareiasaur specimen near Boroviki, with the Vyatka River from the wider Kotel'nich area that would allow direct age determina- at top left. Photographs by A. Yu. Khlyupin. tion (Golubev, 2000). This means that links must be made through cor- relation across country and by using biostratigraphy (Golubev, 2000; 5.2. Dating Goman'kov, 2001). In the Russian magnetostratigraphic scheme (Fig. 6), major normal and reversed chrons in the Upper Permian are

Traditionally, the Russian tetrapod faunas (e.g. Efremov, 1937, named R1P, N1P, R2P, N2P, and R3P, and measurements on many sec- 1941) were dated by comparison with the succession of faunas in tions show that these extend from the base to the top of the Russian the Karoo Basin in South Africa (e.g. Anderson and Cruickshank, Tatarian stage. The three divisions of the Tatarian are matched tenta- 1978; Benton, 1983; Modesto and Rybczynski, 2000) as Late Permian tively to the magnetostratigraphic scale, with the Urzhumian/Severod- and late Tatarian. Comparison of the pareiasaurs (Lee, 2000) and di- vinian boundary falling within N1P and the Severodvinian/Vyatkian cynodonts (Kurkin, 2011) suggests that the Kotel'nich succession is boundary within N2P. The Permo-Triassic boundary is within, but near broadly equivalent to the Pristerognathus Zone, although earlier over- the base, of a normal interval at the top of R3P(Lozovskiy and views (e.g. Kurkin, 2000) correlated the Kotel'nich beds with the Esaulova, 1998; Golubev, 2000; Molostovskiy, 2005; Taylor et al., higher Cistecephalus Zone. This approach is unsatisfactory for two rea- 2009). The succession of repeated reversals in magnetic sense corre- sons: first, the Russian and South African tetrapod taxa are generally sponds to the international Illawarra Hyperchron, which succeeds the 64

Inter- Tetrapod South African Mag. Mag. Russian Sukhona/ North Ostracod Fish Tetrapod national Gorizonts South Urals svitas Vyatka Basin svitas faunal tetrapod stage stages Dvina svitas/ subsvitas zones zones zones Epoch stages complexes assemblage zones Myr Archosaurus RP Molomskaya Komaritskaya Wjatkellina fragiloides- Toyemia blumentalis - Vyazniki Chang. 3 Nizhnefedosovskaya rossicus Nefedovskaya Suchonella typica Isadia aristoviensis Kutulukskaya/ Salarev- Salarevskaya Vyatkian skaya Rovdinskaya Dicynodon 58 (2012) 319-320 Palaeoecology Palaeoclimatology, Palaeogeography, / al. et Benton M.J. Kulchomovskaya Scutosaurus Sokolki Bykovskaya karpinskii 255 N P Erogodskaya 2 Wjatkellina fragilina- Toyemia blumentalis - Dvinella cyrta Strelnia certa Kalikinskaya Kalininskaya Cistecephalus Proelginia permiana Il’inskoye an Kichugskaya Wuchiapingian R2P Sokolki Putyatinskaya Toyemia Tropidostoma Tatarian Suchonellina inornata - 260 tverdokhlebovi - Poldarsskaya Purtovinskaya Prasuchonella inelskaya/ Mutovinia stella stelmachovi ovskaya Isadskaya z Yurpalovskaya Deltavjatia vjatkensis Kotel’nich Pristerognathus

Kotel’nich Strelenskaya Severodvini Malok Illawarra Vya Mikulinskaya Nyuksenitskaya Toyemia Filinskaya Sukhon- Suchonellina inornata - tverdokhlebovae - skaya Dmitrievo Prasuchonella nasalis Platysomus biarmicus Ulemosaurus Isheevo/ Capitanian N P Slobodskaya Tapinocephalus 265 1 Verkhnyaya Tozma svijagensis Malaya Kinel Syr’yanskaya Platysomus biarmicus- Amanakskaya Paleodarwinula

Guadalupian Lopingian Urzhumian Belokholunitskaya Nizhneust’inskaya fragiliformis- Kargalichthys Ilynskaya Prasuchonella nasalis efremovi RP Bolshekinelskaya Estemmenosuchus Ocher Eodicynodon Wordian 1 Maksimovskaya uralensis Morkvashinskaya Paleodarwinula fainae- Kargalichthys Povolzhian/Belebey Verkhneuslonskaya Prasuchonella Kazanian Pechishchinskaya Prikazanskaya tichwinskaja pritokensis Biarmian Kazanian Krasnoyarkaya Amphisites Golyusher- Roadian Sokian/Osinovskaya Kamyshlinskaya Koinichthys Parabradysaurus 270 Baituganskaya tscherdinzevi ivachnenkoi silantjevi Ocher ma Ashalchinskaya Paleodarwinula Sheshmian Starokuakskaya parallelaformis- Acropholis Mordovo-karmalskaya Prasuchonella kargalensis silantievi Ufimian Ufimian Paleodarwinula onica- Platysomus Clamorosaurus Solikamian Faluniella prolata solikamskensis - Inta Kiama Ufalepis magnificus nocturnus Irenian Cisuralian

Kungurian Cisuralian 275 ‘Kungurian’ Filippovian Saranian –

Fig. 6. Stratigraphic summary of the Middle and Late Permian of northern and eastern parts of European Russia, showing the international marine scale with radiometric tie points indicated by black dots (Gradstein et al., 2004; Ogg et al., 83 2008), the international magnetostratigraphic scale (Steiner, 2006), the Russian magnetostratigraphic stages (Molostovskiy 1979, 2005; Khramov et al., 2006; Taylor et al., 2009), the standard Russian gorizonts, biostratigraphic subdivisions of the Ufimian, Kazanian and Tatarian stages, key svitas in the Vyatka basin (Esaulova et al. 1998; Goman'kov, 2001), the Sukhona and North Dvina basin (Golubev, 2000) and biostratigraphic schemes for palynomorphs, ostracods, fishes and tetrapods (Golubev, 2000). Names of svitas are in basic Russian nominative form & all end in -aya, the feminine ending in agreement with the gender of the term Svita. The gorizont and tetrapod biozone terms are anglicised because many are already well established in western literature, such as Ufimian [Ufimskiy], Kazanian [Kazan'skiy], Tatarian [Tatarskiy], Yrzhumian [Urzhumskiy], Severodvinian [Severodvinskiy] & Vyatkian [Vyatskiy]. Tetrapod complexes/biozones are anglicised as follows, using simply the place name from which each is derived, rather than the genitive Russian form: Inta [Intinskiy], Golyusherma [Golyushermskiy], Ocher [Ocherskiy], Isheevo [Isheevskiy], Kotel'nich [Kotel'nichskiy], Il'inskoye [Il'inskiy], Sokolki, Vyazniki [Vyaznikovskiy]. Based on information in Newell et al. (2010). M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 65

Kiama Hyperchron when reversals were rare or non-existent. Compar- 6. Sedimentology ison with the international magnetostratigraphic scale (Steiner, 2006) suggests that N1P may be Capitan N (including P2), R2P includes P3, 6.1. Overview N2P is Chang N (including P4), and R3P includes P5 (Taylor et al., 2009). This review suggests that the Russian Vyatkian (=late Tatarian) is The Kotel'nich red beds occur in near-continuous exposure along broadly equivalent to latest Wuchiapingian and Changhsingian, as the west (right-hand) bank of the Vyatka River, a tributary of the suggested by Grunt (2006), Lozovskiy et al. (2009), and others. An al- Volga which flows south at this point (Figs. 1–4). The sedimentary ternative view, that the Vyatkian is equivalent to the whole of the rocks dip gently to the east, which is evident only to the north of Lopingian (i.e. Wuchiapingian+Changhsingian) has been suggested Kotel'nich town, where the Vyatka flows southwest, before bending by Golubev (in Newell et al., 2010, Fig. 2), but we prefer the former, to the south through most of the section (Fig. 2). Sections were mea- because it is a view of longer standing and it is supported by magne- sured from the water's edge, across the broad, flat-lying beach beside tostratigraphic data (Steiner, 2006; Taylor et al., 2009). the river, and up the cliffs, which range in height from a few metres to The Kotel'nich section apparently falls largely in the palaeomag- 40 m at Agafonovo. The beds lie nearly horizontally in relation to their netic zone of reversed polarity R2P, by comparison with the Sukhona north–south exposure, and so individual beds may be followed along River section (Khramov et al., 2006). The upper boundary of the R2P the eroded riverside platform and the cliff line for long distances. Six magnetozone falls within the Kalikinskaya Packet, and the lower detailed sedimentary logs were taken along a 10 km near-continuous boundary is no higher than the middle of the Nyuksenitskaya Packet. section, from Shestakovy to Zemtsy (Figs. 3, 7), as well as at Port Comparisons to the global standard stratigraphic scale indicate that Kotel'nich, some 10 km north (Fig. 7). the whole Kotel'nich succession is late Capitanian in age (Benton The stratigraphy comprises five main lithological units dominated et al., 2004; Grunt, 2006; Newell et al., 2010). Further, if the Kotel'nich by brown, reddish brown, and grey mudstones of the Vanyushonki tetrapod assemblage is most comparable with the Pristerognathus and Shestakovy members which extend vertically from river level to Assemblage Zone in South Africa (e.g. Kurkin, 2011), new radiometric the top of the escarpment in areas to the south of Zemtsy and north of dates from the Karoo also confirm the age of the latter as late Capitanian Kuznetsy (Figs. 2, 3, 7). Most of the vertebrate fossils are found in the (Rubidge et al., 2010). This then provides a strong indication of the age mudstones of the Vanyushonki Member at relatively low elevations of all other Russian localities that have been confirmed from their fossil close to summer river levels (Fig. 7). Between Zemtsy and Kuznetsy content as belonging to the Kotel'nich or Il'inskoye subcomplexes. the mudstones of the Vanyushonki Member are overlain by fine-

Fig. 7. Logged sections of the river escarpment exposures around Boroviki (see Figs. 2 and 3 for location of sections). The base of the logs corresponds to river level at low summer flows. Vertebrate fossils are primarily found close to river level in a series of mudstone-filled scours cut into a dark red, calcrete-bearing palaeosol within the Vanyushonki Member. 66 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 grained, pale orange, weakly cemented sandstones of the Boroviki right angles. Rootlet structures are commonly highlighted by grey- Member, which form a broadly flat-based, lenticular body that reaches coloured haloes around a black centre or by white calcite mineralisa- a maximum thickness of around 16 m close to Boroviki (Fig. 2). The Bor- tion. Carbonate forms a minor component of the mudstones either in oviki Member and overlying mudstones of the Shestakovy Member are the form of diffuse calcareous horizons up to 1 m thick or as small incised by several bodies of brownish-grey, fine- to coarse-grained (b2 cm) isolated or coalesced nodules which generally occur in sandstone and intraclast conglomerate which infill remarkably steep zones up to 0.5 m thick (Fig. 8B). scours into underlying mudstones and sandstones. These scour-filling Horizons of grey and bluish-grey mudstone vary in thickness from sandstones reach a maximum thickness of 25 m and are named the 10 to 50 cm and generally have an irregular undulating top and an Sokol'ya Gora Member after the large cliff of the same name near Boro- interfingering basal contact with underlying brown or reddish viki. The Chizhi Member is a smaller channel-fill sandstone within the brown mudstones (Fig. 8A). Residual patches of brown or reddish Shestakovy Member distinguished by the preservation of abundant brown mudstone are common in the grey horizons. Grey mudstones plant material and some vertebrate remains in associated grey mud- are generally clayey siltstones with a massive blocky structure and stones. The Kotel'nich red beds are described in upwards sequence of common rootlets. At Boroviki, grey mudstones occur in several clus- the five members named by Coffa (1999): the Vanyushonki, Boroviki, ters of up to 5 beds over an interval of several metres. Shestakovy, Chizhi, and Sokol'ya Gora members. Dark red mudstones occur in two parallel beds spaced 1 m apart at the base of the exposure close to (summer) river level and can be 6.2. Vanyushonki Member traced laterally over several kilometres in the Boroviki area (Fig. 7). The thickness of the dark red units ranges from a few decimetres to 6.2.1. Description 1 m and they contain rootlet structures, small centimetre-scale car- Coffa (1999) named this unit after the village of Vanyushonki, bonate nodules and patches or mottles of grey or bluish grey mud- 18 km south of Kotel'nich on the west bank of the Vyatka River, the stone. The dark red mudstones are relatively clay-rich, with clays site of the first positively identified pareiasaur found by Kashtanov often forming slickensided coatings on the exterior surfaces of angu- in 1933. The maximum thickness seen at outcrop is around 10 m, lar blocks. with an additional 83.5 m subsurface thickness measured from the The stratigraphically higher dark red mudstone is notable for the Kotel'nich borehole, SKV 1. The basal mudstones of the Vanуushonki development of a sharp erosional upper surface that forms a series Member may be traced in surface outcrop to approximately 700 m of scours that partially or entirely cut out the bed (Fig. 8C, D). Scours south of the Kotel'nich River Port where they disappear beneath the vary from broad (several 10s of metres) and shallow to narrow and surface. relatively steep sided and are infilled by pale brown mudstone The Vanyushonki Member is dominated by mudstones (silty clays which, in addition to being a markedly different colour from the un- and clayey silts with small quantities of fine-grained sand) that are derlying dark red mudstone, does not show the development of ex- predominantly pale or moderate brown in colour, but include com- tensive rooting and carbonate nodules. Pareiasaur skeletal remains mon horizons and patches of grey and bluish-grey mudstone and are commonly found within the scour-filling pale brown mudstone, two conspicuous horizons of dark red mudstone at the base of the ex- and this single layer 3–4 m below the sandstones of the Boroviki posure (Fig. 8A). Primary bedding and lamination are not generally Member (Figs. 3, 7) has produced most of the articulated reptile fos- seen in the mudstones, which mostly show an irregular, angular sils formerly assigned to the Kotelnich-1 locality, although skeletons blocky structure. Root traces are common and typically consist of are found at all levels, both above and below the palaeosol horizon, many millimetre-diameter tubules with short branches diverging at and even below the Vyatka River water line. The majority of the

Fig. 8. Photographs showing typical features of the Vanyusonki Member mudstones, (A) alternation of pale brown, grey and moderate reddish brown mudstones, (B) small coalesced carbonate (calcrete) nodules, (C) undulating scour infilled with pale reddish brown mudstone cut into dark reddish brown mudstones with small carbonate nodules and grey mottles and (D) sharp erosional contact between pale brown mudstone above and dark reddish brown mudstone below. M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 67

finds by Sumin from 1990 to 1992 came from this level near the vil- denote the depletion of non-silicate-bound iron under redoximorphic lage Boroviki, but some from near the village Mukha (Ochev, 1995). conditions and they probably represent eluvial-gley (Eg) horizons de- The scours or hollows containing pareiasaurs are roughly circular in veloped in the upper part of the soil profile. Yakimenko et al. (2004) plain view, as determined from individual excavated skeletons, but describe closely comparable grey Eg horizons in Upper Permian it cannot be demonstrated that all skeleton-bearing hollows are circu- palaeosols from the Sukhona River in the northern part of the Russian lar; some might also be channel-shaped. Skeletons are usually intact, platform. Gleying typically results from a raised water table or from but sometimes the lenses contain clusters of well-preserved bones. impeded drainage within the soil profile and appears to contradict The bones are either red-brown or chocolate-black in colour, excel- the evidence for well-drained conditions suggested by the predomi- lently preserved, and with an internal calcite filling. The taphonomy nant red or brown colouration of the mudstones, lack of organic pres- of these remarkable tetrapod finds is discussed in detail below ervation, common rooting and presence of calcretes. Yakimenko et al. (Sections 7.3, 7,4). (2004) explain the coexistence of oxic and redoximorphic features by The mudstones contain a number of thin sandstone beds that are postulating a strongly seasonal, semiarid climate, together with the usually only a few decimetres thick, but can reach 1.5 m. The sand- possibility that precipitation fluctuated on a longer time scale. stones are mostly fine-grained, massive and have sharp lower and Mudstones of the Vanyushonki Member contain several metre- upper boundaries. Coffa (1999) reported 16 fossil tree stumps mea- thick beds of fine-grained sandstone that are generally sharp-based suring from 0.15×0.05 m to 0.4×0.3 m from some of the sandstone and massive. These were probably deposited from relatively uncon- beds. The wood was carbonised and compressed and oriented in var- fined flows, which distributed water and sediment across the flood ious directions, but with a strong west–east component. basin. One sandstone toward the top of the exposure shows a well- developed upward-fining sequence from a basal intraclast conglom- 6.2.2. Interpretation erate, through trough cross-bedded sandstone to a crudely laminated The mudstones of the Vanyushonki Member were probably de- mudstone that contains much plant material. This probably repre- posited from suspension in standing water bodies on floodplains or sents a minor channel fill with the abandoned channel forming a in shallow ephemeral lakes, but the precise environment cannot be long lasting water hole, which allowed the accumulation and preser- determined because of the general absence of primary sedimentary vation of plant material. The abundance of rootlets and large herbi- structure. The presence of pareiasaurs, plant fossils, and ostracods in- vores suggests a relatively humid and well-vegetated landscape. dicates a terrestrial or freshwater environment, with the common oc- currence of rootlets, carbonate nodules (calcretes) and colour 6.3. Boroviki Member horizonation suggesting that deposition was episodic with many ex- tended periods of subaerial exposure and soil formation which oblit- 6.3.1. Description erated most of the primary structure. The predominant brown and Coffa (1999) named this unit after the village of Boroviki, 15 km reddish brown colouration of the mudstones results from oxidation south of Kotel'nich on the west bank of the Vyatka River. It lies con- of iron-bearing minerals during weathering in soils that must have formably above the Vanyushonki Member. The sandbody reaches a been relatively well drained between depositional events, although maximum thickness of around 16 m thick at Boroviki and can be common grey and bluish grey mottles and horizons suggest phases traced over a distance of 10 km along the west bank of the Vyatka of poor drainage and redoximorphic conditions. River from Zemtsy in the south to Kuznetsy in the north (Figs. 2, 3, 7). The two laterally extensive dark red mudstones that occur toward The Boroviki Member is a body of pale orange, weakly cemented, the base of the outcrop at Boroviki are distinctive parts of the stratig- fine- to medium-grained sand. The sandstones are compositionally raphy (Fig. 7). They are relatively clayey with nodular accumulations mature with high quartz content (more than 65%) and a uniform of calcium carbonate and red iron oxides and probably represent the grain size, with more than 90% of grains in the size range 0.05– illuvial (Bk) horizons of moderately developed palaeosols that 0.5 mm, with only 8.5% in the clay fraction as measured by formed during long breaks in sedimentation. Centimetre-scale, micri- Tverdokhlebov and Shminke (1990). The sandbody has a relatively tic carbonate nodules probably represent pedogenic calcretes, given flat, or in places gently downcutting, base and a convex-up top, their association with rooted and colour-variegated horizons and pinching out laterally into adjacent mudstones. Internally the sand- these typically form in well-drained soil profiles in sub-humid, body is characterised by a range of bedding types. To the south, semi-arid and arid climates (Alonso-Zarza, 2003). Given the presence around log position 2 at Boroviki (Fig. 2) the sandbody is 10 m thick of carbonate nodules and the common development of clay coatings and dominated by large-scale, low-angle (15–20°) cross-bedded around peds, the palaeosols could be classified as calcic Argillosols sandstone in thick wedge-shaped sets (Fig. 9A) with distinctive pin- or Calcisols (Mack et al., 1993). The upper palaeosol horizon is spec- stripe laminae (Fig. 9B) and thin granule lags. Further north at log po- tacularly incised by a series of shallow scours which are infilled by sition 3 (Figs. 7, 10B) the basal part of the sandbody comprises small- pale brown mudstones which, although massive, lack the relatively scale trough cross-bedded sandstone with occasional thin rooted mature pedogenic features of the underlying bed and were probably mudstones (Fig. 10), while the upper part includes low-angle lami- deposited rapidly from floodwaters with a high suspended load in nated sandstone and large-scale cross-bedded sandstone with fore- the gullied landscape. Scour systems within successions of floodplain sets dipping toward 050°. The unit may be capped by pale blue fine- mudstones are not uncommon (Kraus and Middleton, 1987), but gen- grained sandstone, 0.4 m thick, corresponding to Bed 4 of Golubev erally require a colour contrast in the eroded and infill materials to be (2000). recognised. At Boroviki these scour fills formed preferential sites for the burial and preservation of pareiasaur skeletons. Microtopography 6.3.2. Interpretation has an important control on the distribution and rate of sedimenta- The Boroviki Member has many features that suggest a predomi- tion across floodplains because lows tend to form the sites of reces- nantly aeolian origin, including the well-sorted, friable texture of sion pondage with higher rates of deposition (Walling and He, the pale orange sandstones, presence of large-scale cross bedding, 1998). High rates of sedimentation are an important factor in the well-developed pinstripe lamination, deflation granule lags and frost- preservation of terrestrial vertebrates because burial prevents skele- ed, pitted quartz grains (Coffa, 1999). There is a corresponding ab- tal remains being destroyed by scavenging or subaerial weathering. sence of features suggesting a predominantly fluvial origin such as Grey and bluish grey bleached mudstones occur as haloes around large-scale channel scours and mudstone intraclasts, although some roots, small mottles and patches within reddish brown mudstones of the small-scale trough cross-bedding associated with rooted mud- and as more continuous horizons (Fig. 8A). Grey colours generally stones at the base of log position 3 (Fig. 7) may have a fluvial origin. In 68 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83

Fig. 9. Photographs showing typical features of the Boroviki Member in the southern part of the outcrop near logged Section 2 (see Figs. 2 and 7), (A) wedge-shaped sets of low-angle cross-bedded, friable, fine-grained pale orange sandstone, and (B) sandstone with well-developed, low angle pinstripe lamination probably deposited by migrating wind ripples. the first sedimentological description, Ignat'ev (1963) interpreted the brown mudstone, commonly grey mottled, alternating with irregular Boroviki sandstones as fluvio-deltaic, and the aeolian interpretation horizons of pale grey mudstone (Fig. 8A). The mudstones are generally was given first by Tverdokhlebov and Shminke (1990), and accepted massive and blocky, with common calcrete nodules and evidence of by Coffa (1999) and Tverdokhlebov (2009). Cross-stratification azi- rootlets and bioturbation. Fragments of the pareiasaur Deltavjatia have muths indicates a general wind direction from the west (Coffa, been found. Fine-grained sandstone beds, generally less than 1 m 1999), with most of the steeper foresets inclined toward the thick, occur throughout, and these are largely massive but occasionally northeast. show a discontinuous horizontal lamination. The geometry and internal structure of the sandbody suggest that it developed as a localised aeolian erg in a floodbasin setting. Thick 6.4.2. Interpretation accumulations of aeolian sands in the upwind (SW) portion of the The Shestakovy Member indicates a return to shallow lacustrine erg pass downwind into flanking areas where the sandbody contains or floodplain conditions, similar to the Vanyushonki Member. The a mixture of fluvial and lacustrine facies. The predominance of rela- combination of red, oxidised mudstones with calcrete and grey re- tively low-angle wind-ripple lamination over steeply dipping aeolian duced mudstones indicates fluctuating drainage conditions. The thin avalanche strata may indicate a relatively wet aeolian system, with a beds of sandstone have been interpreted by Tverdokhlebov (2009) high groundwater table and limited sand supply suppressing the con- as distributary channels within an inland delta or terminal fan. struction of large dunes and favouring the development of low-relief sandsheets and poorly developed mounded dunes (Tverdokhlebov, 6.5. Chizhi Member 2009). Alternatively, the scarcity of steep aeolian cross-strata may re- flect low rates of basin subsidence which favours the preservation of 6.5.1. Description low angle dune aprons close to the water table rather than elevated Coffa (1999) named this the ‘Chizhy Member’ after Chizhi, a khutor, parts of the dune (Fryberger, 1993). The Boroviki Member rests on a or one-settlement village, that is closest to the member, 12.8 km south marked unconformity that cuts out 1–3 m of the underlying Vanyush- of Kotel'nich on the west bank of the Vyatka River. The unit had been onki Member, indicating a phase of cessation of floodplain deposition termed the Chizhebekaya Lens by Russian geologists. We correct the and some erosion. The low relief of the erosion surface and the ab- spelling from Chizhy to Chizhi to match the spelling of the village sence of overlying mudclasts suggest it results from aeolian deflation name, and as used by Russian geologists. The member is a laterally rather than fluvial processes. isolated lens with a thickness not greater than 8 m. In places, it cuts down into the Boroviki Member (Figs. 3, 7). 6.4. Shestakovy Member At the base the lithology is a grey, fine-grained sandstone that overlies an erosion surface covered in reworked mudstone clasts. 6.4.1. Description This passes upward into crudely laminated grey mudstone with Coffa (1999) named the succession of reddish brown and grey abundant comminuted plant and fish debris. mudstones lying above the Boroviki and Vanyushonki members the The unit has yielded a rich macroflora, consisting of carbonised ‘Shestakovo Member’ after the village of Shestakovy, 5 km south of tree stumps, fossilised leaf impressions, and a palynoflora consisting Kotel'nich on the west bank of the Vyatka River. We change the of pollen and spores (Golubev, 2000). The plant fossils reported name from Shestakovo to Shestakovy to match the direct linkage of (Goman'kov, 1996, 1997) are Algites sp. AVG-1, Phyllotheca aff. Turn- place name and stratigraphic unit, as with all the other member aensis, Paracalamites sp., Pecopteris sp. AVG-1, Peltaspermopsis (?) names. The mudstones of the Shestakovy Member are laterally con- sp., Permotheca sardykense Zalessky, Alicospermum sp., Tatarina conspi- tinuous throughout the 20 km exposed southern section, and it may cua Meyen, Persongia beloussovae (Radczenko) Gomankov et Meyen, extend to Port Kotel'nich (see Section 6.7). Member thickness varies Phylladoderma (Aequistomia)sp.indet.,andGeinitzia sp. These are asso- from 5 m to a maximum thickness of 20 m at the southernmost ex- ciated with fish remains, mostly scales, from the organic-rich mud- tent of the section, 18 km south of Port Kotel'nich. In the southern stones near the top of the lens, identified as the actinopterygians part of the section, the Shestakovy Member can locally be divided Platysomus biarmicus Eichwald, Toyemia tverdochlebovae Minich, into two, the Shestakovy-1 and Shestakovy-2 divisions, lying respec- Amblypterina sp., and Watsonichthys sp., as well as ‘Crossopterygii fam. tively below and above the Chizhi Member, an intermittent plant-rich indet.’ (Esin, 1995; Esin and Mashin, 1998). Pareiasaur teeth with 13, in- sandstone lens (Figs. 3, 7). Where the sandstones of the Boroviki stead of 11, cusps, as well as flat osteoderms were found in the Chizhi Member are absent it is difficult to define the bottom of the Shesta- lens in 2009, and these resemble Scutosaurus (‘Proelginia’) rather than kovy Member because there seems to be no interruption in the se- Deltavjatia. Further remains include Suminia teeth, a therocephalian quence of fine-grained red sediments. tooth, teeth and a maxilla with teeth from a gorgonopsian, a canine The primary lithology of the Shestakovy Member is similar to the tooth and vertebra of a dicynodont, and fragments of chroniosuchid Vanyushonki Member, with a predominance of pale brown or reddish osteoderms. These tetrapod fossils, especially the Scutosaurus remains, M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 69

Fig. 10. Photographs showing typical features of the Sokol'ya Gora Member fluvial sandstones, (A) large-scale stratigraphic relationships near logged Section 3 (see Fig. 2 for loca- tion) showing fluvial sandstones of the Sokol'ya Gora Member overlying a high-relief erosion surface cut into pale orange aeolian sandstones of the Boroviki Member. Mudstones of the Vanyushonki Member form the base of the exposure, (B) sharp erosion surface between the brownish grey fluvial sandstones Sokol'ya Gora Member above and the pale orange sandstones of the Boroviki Member below. Basal parts of the Sokol'ya Gora Member contain many large, well-rounded mudstone and sandstone intraformational clasts (C) small to medium sets of trough cross bedding in grey sandstones of the Sokola Gora Member erosively overlying orange sandstones of the Boroviki Member.

suggest the Chizhi lens assemblage equates with that from the Sokol'ya confirm a subaqueous environment and together with the plant taxa Gora Member. and point toward fluviolacustrine conditions (Goman'kov, 1996, 1997). 6.5.2. Interpretation This discontinuous, erosively-based and upward-fining lens proba- 6.6. Sokol'ya Gora Member bly represents a channel fill which following abandonment, for exam- ple by meander cut-off, formed a relatively long-lived pond with 6.6.1. Description poorly oxygenated bottom conditions which accumulated grey lami- Coffa (1999) named this unit after the most prominent sandstone nated mudstones and plant material. The abundant fish remains lens of the member, called Sokol'ya Gora (=‘falcon rock’), located 70 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83

18 km south of Kotel'nich (Figs. 2, 3). A maximum thickness of 90 m (Fig. 7). However, toward the middle of the section, immediately is measured from the top, but this full thickness is preserved only below the dicynodont site, the mudstone is interrupted by a sharp- north of Kotel'nich. It lies unconformably above the Shestakovy Mem- based sandstone bed, 0.1–0.5 m thick, which is predominantly grey ber. The name has been given as ‘Sokolya-gora’ (e.g. Coffa, 1999), but at the base and dark red toward the top. Carbonate concretions be- we correct it to the place name as used by Russians. come common at the top of the sandstone bed. The top contact with The Sokol'ya Gora Member comprises several individual bodies of the overlying mudstone is sharp and planar. The sandstones do not grey and brownish grey, fine-medium grained sandstone that occupy contain any fossils, and these are concentrated in the 2 m of mud- spectacular scours cut into the pale orange aeolian sandstones of the stone immediately above the sandstone bed. Boroviki Member and the fluviolacustrine mudstones of the Vanyush- The Port Kotel'nich section might relate to the main Kotel'nich onki Member (Fig. 7). At Boroviki there are two major scour-filling (southern) section in one of three ways: (1) it could be a lateral grey sandstones that are up to 25 m thick and extend laterally for sev- equivalent of the Shestakovy Member, as Goman'kov (1997), Coffa eral hundred metres (Fig. 3). The sides of the scours are remarkably (1999), and Golubev (2000) argued, (2) it could be a lateral equiva- steep (Fig. 10A) and locally undercut. Flow direction, determined lent of the Vanyushonki Member, also a red mudstone unit and at from cross-sets exposed in three dimensions, is generally toward the base of the main section (Figs. 3, 7), or (3) it could be something the west so the north–south orientated exposures at Boroviki repre- else altogether. Poor exposure between Port Kotel'nich and the main sent a cross section perpendicular to the elongation direction of the section makes it hard to walk out the section and confirm the corre- sandbodies. The sandstones are fine- to medium-grained, locally lation unequivocally. Coffa (1999) noted that the basal ‘sandwich highly micaeous, and at the base contain large reworked clasts of layer’ of the Shestakovy-2 Member in the northern part of the mudstone and pale orange sandstone up to 30 cm in diameter Kotel'nich section disappears underground because the bedding (Fig. 10B). Internally the sandbodies are dominated by sets of trough, dips up-river. Through the lack of recognisable marker horizons, in- and occasionally tabular cross bedding, which are typically 0.1–0.3 m vestigators assumed that the site corresponded to the highest facies thick but can reach 1 m thick (Fig. 7). These are typically grouped into of the Vanyushonki Member, but detailed observation of the outcrop cosets 1–2 m in thickness (Fig. 10C), which may have a basal erosion south of Gorodishe revealed that the base of the Shestakovy-2 Mem- surface overlain by an intraclast conglomerate. Some cosets are ber could be traced along the lower part of the Vyatka River bank. In a capped by thin units of highly micaeous, flat-laminated fine-grained bank exposure cleared by a creek just south of the dicynodont site at sandstone. Convolute bedding is common in the centre of the sand- Port Kotel'nich, the most northern appearance of the ‘sandwich layer’ body exposed at log position 3, while the tops are characterised by was observed, only 1.5 m higher than the water level of the Vyatka layers and nodules of carbonate cementation and interbedded red- River during the summer of 1997 (Coffa, 1999). dish brown mudstones. We confirm the view presented by previous authors, that the base Rare, disarticulated fossil bones and occasional bivalves are found of the Port Kotel'nich section lies within the Shestakovy Member, but in the fluvial sandstone of the channels. The tetrapod remains have the correlation of the top is debated. Goman'kov (1997) presents the been identified as Chroniosuchus levis, Proelginia cf. permiana (=Scu- most thorough case, using the 200-m deep SKV-1 borehole at tosaurus karpinskii), Proburnetia viatkensis, and Dvinosaurus primus, Kotel'nich (Ignat'ev, 1962, pp. 222–223) to provide the link from all typical of the Il'inskoye Subcomplex, the basal Vyatkian unit the southern Kotel'nich section (Fig. 3) to that at Port Kotel'nich (Fig. 6; Golubev, 2000, p. 87). The upper red mudstones (Golubev's (Fig. 7): he correlates the borehole depth 83.8 m with the top of the bed 8) are characterised by an extensive invertebrate fossil assem- Chizhi Member, and the ground surface roughly with the Sokol'ya blage, comprising ostracods and bivalves. Gora Member, even though that conglomeratic unit is represented only by a thin band in Goman'kov's section. Then, he argues that the 6.6.2. Interpretation Port Kotel'nich section is higher, with the base equivalent to the The grey and brownish grey sandstones of the Sokol'ya Gora Shestakovy-2 Member, and the 15-m borehole depth matching a Member show many features that suggest a fluvial origin, including transition from siltstone to sandstone near the base of the Port an abundance of large- and small-scale scouring, intraclast conglom- Kotel'nich section. Golubev (2000, p. 118) also makes the Port erates, trough cross-bedding, and abundance of mica. The sandstones Kotel'nich section equivalent to his bed 6 (=Shestakovy Member), were deposited in deep scours that were incised up to 25 m into the and places it below his bed 7 (=Sokol'ya Gora Member). As underlying aeolian sandstones and fluviolacustrine muds. The pres- Goman'kov (1997) indicates, regional dips mean that it is perhaps ence of numerous erosion surfaces and intraclast conglomerates not appropriate to assume that the Port Kotel'nich section (Fig. 7) within the scours suggests that these were not cut and filled in a sin- simply sits in its entirety on top of the Sokol'ya Gora Member, but gle event but acted as long-term conduits for multiple flow events. that much of it is laterally equivalent to those upper members. The gradual abandonment of these flow paths is marked by decreas- ing grain-size and extensive carbonate cementation toward the top 6.8. Synthesis of depositional systems shown in the Kotel'nich exposures of the sandbodies. The westerly flow direction is consistent with the mineralogy of the sandstones, which indicates a heterogeneous meta- The Permian exposures south of Kotel'nich show a remarkable morphic source in the Ural Mountains to the east (Coffa, 1999). These range of sedimentary facies within a relatively thin stratigraphic in- sandbodies appear to have been deposited by major fluvial distribu- terval and include mudstones deposited in shallow fluviolacustrine tary channels carrying water and sediment hundreds of kilometres environments that were subject to numerous episodes of sub-aerial from their Uralian source far west onto the Russian Platform. exposure and soil development, aeolian sandstones, and deeply- incised fluvial channel-fills. The environmental story recorded by 6.7. The Port Kotel'nich section the Kotel'nich outcrops starts with relative geomorphic stability and the formation of mature and laterally-extensive dark red, rooted An excellent high exposure of red beds is seen at Port Kotel'nich, palaeosols with calcretes on what must have been a well-vegetated and it extends 400 m south to Gorodishe (Figs. 2, 4B, 7). The site and well-drained floodplain (basal Vanyushonki Member). This was excavated from 1990 onwards, and over 70 skeletons and bone phase of stability was brought to an abrupt end by a high magnitude associations were discovered, nearly all of them dicynodonts flood event that scoured the surface of the floodplain and deposited a (Kurkin, 2000, 2011). Most of the Port Kotel'nich section comprises layer of mud, which was locally of sufficient thickness to encase and relatively homogeneous pale brown and reddish brown mudstones preserve many complete pareiasaur skeletons. Further aggradation with grey mottling and calcrete nodule horizons at regular intervals of fluviolacustrine mudstones was terminated by the development M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 71 of a local aeolian dune field (Boroviki Member), which migrated Table 1 across the eroded surface of the former floodbasin. It is uncertain Faunal composition of the Kotel'nich locality, Russia (Vanyushonki Member), based on collections made since 1990. Abbreviations: Del, Deltavjatia; Eme, Emeroleter; whether this was caused by a change toward greater climatic aridity, Insect., Insectivores; Sum, Suminia;The,Therocephalia;Via,Viatkogorgon.*means fl or simply a shift in the position of the active oodbasin away from unknown number of skeletons in accumulations. Table from Il'ya Shumov, updated from Kotel'nich. The return of fluviolacustrine sedimentation to the version in Fröbisch and Reisz (2009). Additional identified materials come from other Kotel'nich area is initially marked by mudstones (Shestakovy Mem- localities and members, as follows: Port Kotel'nich: the dicynodont Australobarbarus ber) and thin channel sandstones (e.g. Chizhi Member), but then by (83 specimens, collected as follows: 1991 (2), 1992 (32), 1993 (12), 1994 (3), 1995 fl (1), 1996 (1), 1997 (26), 1998 (3), 2002 (1), 2009 (2)); Shestakovy Member (Deltavjatia, the incision of major uvial conduits (Sokol'ya Gora Member), 3, collected 1995, 2002, 2008; Dicynodontia indet.,1, collected 2008); Chizhi Member (one which eroded deeply into underlying deposits. These westward- Scutosaurus collected 2007; all others 2009: Scutosaurus,2;Suminia,1;Dicynodontia flowing rivers probably record the abrupt shift (avulsion) of channels indet., 1; gorgonopsian, 2; Chroniosaurus, 1); Sokol'ya Gora and Agafonovo lens (Scuto- into the Kotel'nich area, which may have been cutting a pathway saurus, 1 [1996]; Therocephalia indet., 4 [1995–6]; Dvinosaurus, 1 [1996]; Chroniosaurus, 1 [1996]), and Iskra, 7 km north of Kotel'nich (Dicynodontia indet., 1 [1995]). through the Kotel'nich depositional lobe to establish new floodbasins at more distal, topographically lower, locations on the Russian Diet Herbivores Insect. Carnivores platform. Year Del Sum Eme The Via 1990 14 4 ––– 7. Kotel'nich tetrapod assemblages 1991 18 1 – 1 – 1992 16 10* 1 2 2 1993 7 5 2 3 – 7.1. Tetrapod-bearing horizons 1994 18 13* 2 7 1 1995 7 2 2 5 – As noted earlier, tetrapod fossils occur at three levels in the 1996 6 1 – 31 Kotel'nich section. The isolated detrital bones in the plant-bearing 1997 2 * 1 –– mudstone conglomerates of the Chizhi lens and the basal intraclast 1998 6 5* 3 2 2 1999 10 22* – 3 – conglomerates and cross-bedded sandstones of the Sokol'ya Gora 2000 11 3 – 5 – Member are not further considered here. Their preservation is uncon- 2002 5 2 1 –– troversially explained as a result of high-energy channelized flows 2004 6 1 ––1 – that entrained or reworked carcasses or isolated bones from older 2005 2 2 2 1 2006 3 –– –– bank materials, as well as plants and invertebrates in certain cases, 2007 9 3 2 2 – and transported them some distance before burial. 2008 3 3 – 2 1 Here, we focus on the preservation of complete skeletons, and 2009 3 1 – – – there are two occurrences: 2010 3 1 – 1 – Totals 149 79 16 36 9 (1) The great majority of fossil tetrapods from Kotel'nich come Totals (%) 51.6 27.3 5.5 12.5 3.1 from the Vanyushonki Member, the basal red mudstones, and Diet grp. (%) [289] 78.9 5.5 15.6 they are typically labelled ‘Kotel'nich’, even though most come from locations some distance south of the town. Further, 7.2. Dicynodont skeletons at Port Kotel'nich the majority of recent finds, from the 1990s onwards, have come from this level, along the west bank of the Vyatka River At the Port Kotel'nich locality, probably within the Shestakovy from Zemtsy to Shestakovy villages (Figs. 2, 3). Member (see Section 6.7), numerous dicynodont skeletons (Australo- (2) The lower parts of the red mudstones at Port Kotel'nich have barbarus) were excavated in the early 1990s (Kurkin, 2000). All 86 also produced fossil tetrapods, namely the dicynodontid Tropi- skeletons came from a single layer about 0.5 m thick. Some of the re- dostoma and the pareiasaur Deltavjatia cf. vjatkensis. mains were individual pieces, such as isolated skulls or jaws, and Recent collecting, since 1990, has yielded more than 390 skeletons other elements. However, many of the finds were complete skeletons and partial skeletons of tetrapods, of which 290 come from the often forming clusters, consisting of the bones of one or two individ- Vanyushonki Member (Table 1; Modesto and Rybczynski, 2000; uals. Some showed an unusual orientation of the skull and skeleton, Fröbisch and Reisz, 2009). The fauna is dominated numerically by as if the skull had been anchored in the sediment by the canine herbivores, comprising 79% of the specimens, and small numbers of teeth, and the postcranial skeleton moved more freely in the flowing the insect-eating Emeroleter (5%), as well as small (12%) and large water. In one case, a dicynodont skeleton was found lying on its right (3%) carnivores. Among herbivores, there are numerous articulated side, with its legs underneath. Another skeleton was buried in an skeletons of the larger pareiasaurs (52%) and the small Suminia (27%). inverted position, with the backbone arched. Entirely unlike the par- Ochev (1995, p. 57) reported on the skeletons collected from the eiasaur skeletons in the Vanyushonki Member, there is only one case Vanyushonki Member: of a large specimen of a dicynodont found standing on its legs, as if preserved in life position. The abundance of thin layers of sandstone ‘… most of the skeletons are concentrated at levels that are locat- in the clay marl with the remains of dicynodonts, as well as the ed in bone-bearing deposits, from 3 to 4 m below the overlying large number of calcareous concretions and pellets indicate that sandstones [of the Boroviki Member]. In addition to numerous in- these carcasses had all been transported to a greater or lesser extent, dividual skeletons in varying degrees of preservation, at Kotel'nich presumably by rivers, and then dumped in waning currents. were also found several clusters of isolated bones of several indi- viduals, among which sometimes co-exist relatively large remains 7.3. Taphonomy of therapsid skeletons in the Vanyushonki Member of pareiasaurs and smaller animals, therapsids. It is possible that some of these clusters, occurring in the laminated rock, were The smaller reptiles in the Vanyushonki Member are found either as formed by the movement of bone flows.’ isolated pieces or, in the case of Suminia, sometimes as assemblages of skeletons, a monotaxial, monodominant bonebed (Eberth et al., 2007). In the description below, we deal first with the preservation of the Ochev (1995, p. 57) noted further: ‘The death of the Suminiastook Port Kotel'nich dicynodonts, then the smaller skeletons in the place in their life positions — with their backs looped by bending the Vanyushonki Member, before focussing on the extraordinary preser- body. The theriodont died, fell on his side and stiffened, with the back- vation of complete pareiasaur skeletons in the Vanyushonki Member. bone straightening, the legs and tail outstretched, and with the head 72 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 lightly bent down. These poses quite definitely indicate a place of death be measured, all have the head oriented from 0 to 180°, and six have near the burial spot.’ Fröbisch and Reisz (2009) illustrate a remarkable the head oriented from 0 to 60°; none of the specimens is oriented in block containing at least 15 individual Suminia skeletons (PIN 2212/ the 180–360° quadrants. The rose diagram (Fig. 11C) has a mean orien- 116; Fig. 11), and they note that the skeletons were well preserved tation of 68.84° for all ten specimens, and the orientations are non- and show little sign of weathering, predation, or scavenging, and so random, indicating a preferred orientation (R=0.636, p=0.014; were presumably buried rapidly, ‘possibly as a result of a catastrophic chi-squared=13.2, p=0.004). event’. Six of the 15 identified skeletons (specimens 1–5, 11) are ap- The alignment of skeletons may have been produced by current proximately aligned, with two curled up (specimens 6, 12), two roughly flow at the site of death or following short-distance transport. The at right angles (specimens 10, 13), and five incomplete and uncertain incomplete specimens may have lost bones by current winnowing. (specimens 7–9, 14, 15). Of the ten specimens whose orientations can Despite Ochev's (1995) suggestion that the various straight-backed

Fig. 11. Suminia getmanovi, large block with articulated skeletons. (A) Photograph and (B) colour-coded outline drawing of PIN 2212/116, showing the presence of at least 15 specimens. (C) Rose diagram, showing distribution of the ten specimens (numbers 1–6, 10–13) for which orientations could be assessed; orientations were measured as the angle of a straight line aligned with the dorsal vertebral column, from pelvis to neck, measured in degrees from zero (pointing right). M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 73 and curved skeletal postures indicate death positions, it is not clear infilled by pale brown, locally grey mottled, massive blocky mud- that these features can be used to distinguish such an interpretation stone which contrasts with the underlying dark red or reddish from the more likely suggestion that the carcasses were transported, brown palaeosol with calcrete nodules (Fig. 8C, D). These overly- or moved and winnowed, under the influence of water currents. ing pale brown massive mudstones do not show any of the col- our stratification or calcrete nodules of the underlying mature 7.4. Taphonomy of pareiasaur skeletons in the Vanyushonki Member palaeosols. This suggests relatively rapid deposition. The actual process (e.g. massive sediment flows or from suspension) is im- 7.4.1. Description possible to determine because all the primary structure has been The numerous complete pareiasaur skeletons from Kotel'nich have removed by weak pedogenesis. However, because the mud- fi attracted most attention in previous accounts. First, the key features of stones were only weakly modi ed by soil-forming processes it these skeletons from the Vanyushonki Member will be enumerated, is likely they were deposited rapidly as a relatively thick bed. – – and then the most likely model for their preservation will be developed, (2) Usually just one sometimes two bodies per hollow: More than fi by comparing a range of possible models. 90% of pareiasaur nds consist of a single skeleton per hollow. The Kotel'nich pareiasaur skeletons, most of which occur at one ho- In 1999, two pareiasaur skeletons were found in a single fi rizon in the Vanyushonki Member, show a number of characteristics: mudstone- lled hollow, one lying on top of the other (KPM (1) the skeletons all sit in hollows scoured into a palaeosol surface; 234, Fig. 14E). The upper skeleton was buried with its back (2) there is usually just one – sometimes two – skeletons per hollow; downwards, and the lower skeleton, preserved complete, lay (3) the skeletons are remarkably complete and articulated; (4) the beneath at the bottom of the pit, with its legs sprawled to the skeletons are almost never belly-up; (5) the bones sometimes show side and its backbone arched. evidence of exposure; (6) the animals are of uniform size, and small; (3) Skeletons are remarkably complete and articulated: All older re- and (7) pareiasaurs were terrestrial herbivores. These observations cords, outlined above, and more recent excavations, have con- fi will be explained further. rmed the remarkable completeness of the individual pareiasaur skeletons. Ochev (1995, p. 57) and Sumin (2009) (1) Skeletons all sit in hollows on a palaeosol surface: The preservation report from their first-hand observations of the 1990–2 exca- of complete pareiasaur skeletons is unusual and localised. They vations that 23 of the skeletons were fully articulated, and occur in mud-filled hollows, the majority of them on a single nine were associated clusters of scattered bones, each from a palaeosol horizon, some 3–4 m below the contact with the over- single individual. The majority of specimens though were so lying sandstones of the Boroviki Member (Figs. 3, 7), a fact complete that they retained the dermal ossicles in situ on the noted before (Ochev, 1995; Tverdokhlebov and Shminke, back and all hand and foot elements intact — commonly 1990; Tverdokhlebov, 2009). This skeleton-rich horizon is these small elements become detached and can be removed marked by a narrow bench standing out as a slightly positive by low-energy currents (Eberth et al., 2007). Although most feature, because the palaeosol horizon is indurated with car- of the skeletons are in good condition (Figs. 13, 14), they all bonate, and it extends for several kilometres along the fore- show some damage: some lack one or both hands, feet, legs, shore of the Vyatka River, close to water level (Fig. 12). the front part of the skull or lower jaw. These small marks of The hollows are 3–5 m wide and 1.5 m deep, and in places they damage are not a result of poor excavation, but were inflicted are closely spaced, some 1–10 m apart, and many of the hollows pre-burial either by scavenging or weathering of the carcass. at this level do not contain skeletons or bones. The hollows are Evidence for scavenging may include the discovery of a

Fig. 12. Excavation of vertebrate fossils in 2009 from pale brown mudstones of the Vanyushoni Member, erosively cut into the dark reddish brown palaeosol below. Dashed lines in (A) mark the extent of the palaeosol horizon, and the field workers are beginning to plaster a pareiasaur skeleton found in a scour on top of the palaeosol. (B) Plastered skeletons of [i]Sumnia[/i] on top of the palaeosol, ready to be lifted. The crew are excavating the next specimen, some 12 m away. 74 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83

upwards (Figs. 13B, C, 14A, B, D–H). The commonest position, with the dorsal side facing up, the head and tail down, and the limbs vertically below, with the feet down (Fig. 13B, C), led early discoverers (e.g. Hartmann-Weinberg, 1933, 1937; Kashtanov, 1934) to suggest the animals had died while stand- ing up, and with their feet stuck in the mud. In many skeletons the vertebral column was arched — it was this feature that Hartmann-Weinberg (1937) interpreted as ‘a swimming pose’. In some cases, the skeletons are at an angle to the bed- ding planes, with the limbs down on one side only and up on the other, or with the head and front quarters up (Fig. 13C), and the rear quarters at the base of the hollow. These observations are confirmed by recent work in which more than 40 skeletons were observed in situ (Khlyupin et al., 2000; Khlyupin, 2007; Sumin, 2009). These authors note that most skeletons were found as if standing upright in the mud, and without any signs of transport (Figs. 13, 14). Only two specimens have been noted preserved belly-up. One (KPM 5/97; Fig. 14B) was badly damaged, suggesting that, un- like the others, this skeleton had been preserved on the flat surface, and not in a hollow, and had been predated and weathered, so causing an unusual level of damage. In 1998, near the village of Mukha, a small pareiasaur skeleton (KPM 286; Fig. 14A) was found, also lying on its back, with the limbs offset to one side and the ribs virtually absent. This par- tial skeleton lay in grey-coloured clay marl, containing numer- ous scattered bones of small reptiles and carbonised plant remains, evidence perhaps of water transport. This upright posture was noted also by Sander (1992) in his study of Late Triassic Plateosaurus bonebeds of central Europe. (5) Bones may show evidence of exposure: In some cases, the bones appear to be bleached, perhaps suggesting that they were ex- posed at the surface for some time prior to burial (Ochev, 1995), but they might just as well have been altered by groundwater or diagenesis. One recently excavated specimen consisted of a well-preserved postcranial skeleton, but with a fragmentary skull lying in pieces at the front of the vertebral column. The context of the skeleton in the field suggested that the body was in the hollow and covered with sediment, while the head remained exposed for some time, when it may have been attacked by scavengers or weathered. (6) Animals are of uniform size, and small: The Kotel'nich pareia- saurs all belong to one taxon, Deltavjatia vjatkensis (Hartmann-Weinberg, 1937), named originally as a new spe- Fig. 13. Photographs of prepared specimens of Deltavjatia vjatkensis, as preserved: cies of the South African genus Pareiasuchus. Over the years, (A) skeleton lying on its side, KPM 290; (B) skeleton lying belly-down and with the additional species names were given to Kotel'nich material – limbs outstretched, KPM 232; (C) close-up of skeleton, with head and forelimbs raised, Anthodon rossicus Hartmann-Weinberg, 1937, A. chlynoviensis KPM 289. Photographs by Al'bert Yu. Khlyupin. Efremov, 1940 – but these all belong to the one taxon (Ivakhnenko, 1987; Lee, 2000). D. vjatkensis is a moderate- fragment of a small predator's tooth – possibly from a therio- sized pareiasaur, about 2 m long, smaller than the other fa- dont – found near one skeleton (Ochev, 1995), but predatory mous Russian pareiasaur Scutosaurus karpinskii (Amalitskiy, teeth are not at all as common at Kotel'nich as reported by 1922), which is typically 3 m long. Scutosaurus was the first Sander (1992), for example, around the postulated mired Pla- pareiasaur to be found in Russia, and Deltavjatia was always teosaurus of the Late Triassic. said to be small in comparison. This presumably gave rise to Pareiasaur skeletons from coeval deposits elsewhere, such as the repeated statement that the Kotel'nich pareiasaurs are ju- those from the Sokolki locality on the banks of the North veniles (e.g. Hartmann-Weinberg, 1937; V'yushkov, 1953; Dvina River, south of Kotlas collected by Amalitzkii in the Ochev, 1995), an assertion that is clearly unjustified. This early twentieth century are also remarkably complete (Ochev casts doubt on earlier claims by these authors that the and Surkov, 2000), but these deposits were more typical fluvi- Kotel'nich site shows evidence of selective trapping of a juve- atile assemblages with piles of skeletons in close association nile size class and that the larger adults managed to escape be- within coarse channel sands. cause they were stronger. All that can be said is that the (4) Skeletons are almost never belly-up: The posture of the skele- Kotel'nich pareiasaurs belonged to a single species, D. vjatken- tons is particularly interesting: they are nearly always pre- sis, and that this species was rather smaller than the geologi- served belly-down or on their sides. Of 14 complete skeletons cally younger S. karpinskii that lived some 300 km to the north. recorded in situ, Ochev (1995) noted that four were lying on (7) Pareiasaurs were terrestrial herbivores: Pareiasaurs were stocky their sides (Figs. 13A, 14C) and eight were buried back- animals, with rather massive bodies, short legs and tails, and M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 75

Fig. 14. Drawings of recently excavated pareiasaur skeletons from the Vanyushonki Member at Kotel'nich. Specimens are KPM 286 (A), field number KPM 5/97 (B), KPM 26 (C), KPM 23 (D), KPM 234 (E), private collection, traded by ‘Stone Flower’ in the 1990s (F, G), Museum “Exportsamotzvety”, Moscow (H). Drawings made after collection and specimen preparation by Al'bert Yu. Khlyupin.

an armoured head (Fig. 15A). Their relatively small, somewhat and sides of watercourses and lakes (Fig. 15C). Evidence in fa- leaf-shaped teeth indicate a herbivorous diet, supported also vour of the terrestrial life mode and against the swimming by their massive trunk capable of housing a vast gut. They ran- mode comes from their limb morphology and from abundant ged in length from 0.6 to 3.5 m, the larger ones weighing per- tracks formed in the same way as the majority of other Middle haps 600 kg. The majority of interpretation of pareiasaur and Late Permian tracks, in slightly damp, but not submerged, palaeobiology is that these were terrestrial animals, capable mud (Gubin et al., 2003; Voigt et al., 2010). Deltavjatia is a of efficient semi-erect locomotion (Lee, 2000; Sumida, 2001; basal pareiasaur in phylogenetic terms (Lee, 2000), being smal- Fig. 15B). An alternative view was, however, promulgated by ler and less armoured than more derived forms. Ivakhnenko (1987), Gubin (1989), and Khlyupin (2007), that pareiasaurs were essentially aquatic, being similar to the mod- 7.4.2. Hypotheses of burial ern dugong in spending most of their time in relatively deep The skeletons of the pareiasaurs at Kotel'nich largely occur in water, swimming and feeding on water plants at the bottom hollows on top of a palaeosol unit in the Vanyushonki Member. 76 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83

stuck in the thick mud at the bottom of the lake, and so could not rise as decomposition gases filled the belly. This view is rejected here because there is no evidence for deep lacustrine environments in the Vanyushonki Member. With the excep- tion of local grey mottling, the mudstones are well oxidised and show calcretes and rootlets, evidence for frequent epi- sodes of extended subaerial exposure. (2) Killed by desertification events: The alternative ‘underwater’ view, expressed by Ivakhnenko (1987) was that the more or less fully aquatic pareiasaurs died when their ponds dried up periodically. This model does not necessarily imply miring, but does suggest that the pareiasaurs either could not flee the drying conditions, or that the drying happened too fast for them to escape to another pond. This model is unlikely, how- ever, because pareiasaurs were almost certainly terrestrial an- imals, and so could walk from lake to lake. (3) Buried under sand dunes: The Boroviki Member sandstones are aeolian, indicating an advancing dune field over the alluvial sediments of the Vanyushonki Member. The close proximity of these aeolian sands, 3–4 m above the pareiasaur-bearing ho- rizon could suggest death under an advancing dune field, as has been suggested for tetrapods in the Late Triassic Lossie- mouth Sandstone in Scotland (Benton and Walker, 1985) and the Late Cretaceous of Nemegt, Mongolia (Loope et al., 2001), although this has not been proposed in print for the Kotel'nich tetrapods. This would in any case be unlikely because the sed- iments above the pareiasaur-rich horizon are fluviolacustrine (Figs. 7, 8), and so the tetrapods died some long time before the sedimentation regime switched temporarily from alluvial to aeolian. (4) Trapped in burrows: Sumin (2009) suggested that the pareia- saurs were trapped in burrows. As evidence, he noted the ex- cellent preservation of the skeletons, the fact they seemed to occur in distinct hollows in the sediment, and that they were reptiles living in a highly seasonal, tropical environment with distinct dry seasons. He did not refer to the fact that this is in- deed a key mode of preservation of tetrapod skeletons in anal- ogous sedimentary settings of similar age in South Africa (Smith, 1987, 1993; Groenewald et al., 2001; Damiani et al., 2003; Abdala et al., 2006; Modesto and Botha-Brink, 2010;

Fig. 15. The anatomy and reconstruction of pareiasaurs. (A) Mounted skeleton of the Bordy et al., 2011). None of these reports from the Karoo iden- geologically younger pareiasaur Scutosaurus from Sokolki on the North Dvina, as tified burrowing pareiasaurs, however; the fossil evidence mounted at PIN. (B, C) Life reconstructions, as a terrestrial (B), and aquatic, dugong-like shows that the Karoo burrowers were dicynodonts, cynodonts, animal (C). A, Photograph by AYK; C, drawing by Y. D. Kalganov. and procolophonids. Importantly, however, the field data from the excavation of 390 skeletons at Kotel'nich since 1990 has shown no evidence of burrow structures around the skeletons based on comparisons with the convincing burrows in the The taphonomy of these strikingly complete skeletons has been Permo-Triassic of the Karoo. Admittedly, abandoned burrows interpreted in eight ways, as: (1) stuck in the mud of deep lakes; that collapse before infilling has begun may be hard to detect (2) killed by desertification events; (3) buried under sand dunes; (Smith, 1993), but there is no evidence at Kotel'nich of impres- (4) trapped in burrows, perhaps following hibernation; (5) car- sions of nesting material on a scratch-marked surface, or artic- casses dumped in fluviatile scours; (6) animals caught in hollows ulated skeletons in typical hibernation pose, as found in the while digging for water; (7) animals trapped in shallow wallows; Karoo sediments. Our main reason for doubting that any of or (8) animals mired when weakened by an arid season. These the skeletons from the Vanyushonki Member at Kotel'nich eight models will be considered in turn. were preserved in burrows is that the hollows in which the (1) Stuck in the mud of deep lakes: Gubin (1989), who interpreted pareiasaur skeletons sit are shallow and do not extend over pareiasaurs as aquatic (see above), argued that their carcasses the skeletons: the sediments above are laminated alluvial became trapped in the mud on the floor of a deep lake. He sug- mudstones and siltstones that drape over the hollow and skel- gested that the back-upward posture of most of the skeletons, eton in continuity. This absence of burrows at Kotel'nich is and especially those with the legs on one side down and one somewhat unexpected, as all complete skeletons from the side up, indicated that the animals were already dead when Permo-Triassic of the Karoo, whether curled up or with a they became stuck in the mud, and that they were not strug- straight backbone, have been interpreted (Smith, 1993) as pre- gling to free themselves. Gubin (1989) argued that the pareia- served in burrows. Note, however, that only 10% of a sample of saurs had died for any number of reasons, while swimming 329 Karoo skeletons fell into Smith's (1993) two ‘complete about in the lakes, and the carcasses sank to the bottom skeleton’ taphonomic categories, compared to the much higher under the influence of their heavy weight. They then became percentage among the 390 Kotel'nich skeletons. M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 77

(5) Carcasses dumped in floodplain scours: A further suggestion is evidence that medium-sized and large mammals today dig that the pareiasaur carcasses were entrained, transported and holes for water in drying conditions, there are no records of deposited by a major overbank flood event. As the carcasses those animals being trapped in the holes, or dying in such a were moved slowly by low-energy flows in shallow water, it manner that individual carcasses would be distributed one could be that they lodged in erosive scours produced by earlier, per hole. The holes are not so deep, nor the animals so weak, stronger currents. As evidence, it might be noted that complete that they cannot climb out and walk away. pareiasaur skeletons in hollows may be associated with isolat- (7) Trapped while wallowing: Large mammals today, such as buffalo, ed bones, accumulations of bones, or complete skeletons of pigs, and elephants may create shallow hollows around their smaller contemporaries. For example, under the skull of one bodies as they wallow. Wallowing is partly to cool down in hot of the recently excavated pareiasaurs (Fig. 14G), a complete weather, and partly to dislodge parasites. Perhaps pareiasaurs skeleton of Suminia getmanovi was found, together with an iso- also wallowed when there was enough water in the mud, and lated, crushed mandibular bone of a pareiasaur, and two bro- their wallow holes retained their depth because of the semi- ken ribs probably from a gorgonopsian. Other rare examples consolidated palaeosol substrate. It is unlikely, however, that of this kind have been noted earlier, including the 1998 skele- the animals would have become trapped in such shallow hollows ton from Mukha (KPM 286; Fig. 14A), which was unusually on unless they were weakened by hunger and drought. its back, and associated with water-transported bones of small (8) Mired in soft sediment: This leads us back to a version of the first reptiles and plant remains. A further pareiasaur skeleton found proposal about the unusual preservation of the Kotel'nich car- in 1994 below the village of Nizhnaya Vodskaya (KPM 23; casses (Hartmann-Weinberg, 1933, 1937; Kashtanov, 1934; Fig. 14D) was lying on its left side, and the backbone was bro- Khlyupin, 2007), which was that the pareiasaurs had become ken into several fragments, abutting each other, as if the skele- trapped in boggy muds, and they were preserved more or ton of the animal had been twisted several times along the less in situ. The evidence is the posture of most of the skeletons longitudinal axis. Further, ribs and small bones of the skeleton, with the dorsal side facing up and the limbs down, as if they including the phalanges and the tail vertebrae, were missing. It had died standing, as well as the excellent quality of preserva- is not certain whether these disturbances were caused by tion. These authors also suggested that the animals had been transport or by scavenging. However, such finds are rare, and alive when they were in the hollows, and indeed were trying most pareiasaur skeletons are complete, back-upwards, and to escape: some skeletons were at an angle to the bedding apparently standing in their hollows. planes, either with the limbs down on one side and up on the The possibility of water-borne transport of the carcasses has other, as if they had been flailing in a mud bath, or with the been rejected, or not even mentioned, by most previous au- head and arms up on the edge of the hollow and the feet on thors. Sumin (2009), for example, noted that there is little ev- the bottom, as if trying to climb out of a hole head-first. Finally, idence for transport and dumping because the skeletons are the size range of animals was said to suggest that the larger an- isolated and not preserved in overlapping masses, there is little imals had been strong enough to escape, while tiny juveniles evidence for massive erosion that might be associated with either never entered the area or were small enough not to get currents strong enough to carry the bulky carcasses, the car- stuck. As noted earlier, there is no evidence that the Kotel'nich casses ought to be associated with massive boulders, tree pareiasaurs are not all normal-sized adults. trunks and other large objects indicative of high-energy flow, and the carcasses would surely be oriented randomly, some We do not accept a pure miring model, where the mud itself was belly-down, some belly-up, and some on their sides. Here, somehow so tenacious that the animals, in normal, healthy condition Sumin (2009) makes the assumption that large objects such somehow became stuck. However, Ochev (1995), Khlyupin (2007), as tree trunks and coarse sediment grades were actually avail- and Tverdokhlebov (2009) presented a plausible modification in able for transport, which is unlikely given the distal, fine- which the animals all died at the same time during a particularly dev- grained floodplain/lacustrine setting and he also limits himself astating aridification event. In the wet season, herds of pareiasaurs to considering only high-energy flows, and not more gentle ranged over the flat plains, feeding on waterside plants. As conditions water movement over a consolidated palaeosol surface that became worse at the onset of the dry season, the pareiasaurs congre- might resist erosion. It is therefore possible that some car- gated around remaining ponds, and smaller and weaker animals died. casses were moved by later water movement, and dumped in As the ponds dried out completely, soils were formed. Ochev (1995) the hollows following short-distance transport, although this also argues that the deaths probably did not happen en masse, as a does not explain the consistent belly-down orientation. single, sudden catastrophe, but that the pareiasaur carcasses accumu- (6) Animals caught in hollows while digging for water: Perhaps the lated over some time. pareiasaurs were digging down for water, or roots, and created the hollows in which they are now trapped, and many failed to escape. The pits might have been long-term structures, exca- 7.5. Miring as a cause of death vated to shallow depth initially to allow water to pool, and then visited time after time, and deepened progressively to Miring is commonly cited as a means by which large terrestrial reach water as the dry season continued. Eventually, the hole animals can become trapped (Rogers and Kidwell, 2007), and modern became too deep, and the last animal, or animals, to try to examples (e.g. Weigelt, 1989; Mellink and Martin, 2001)showhow reach water was trapped, some indeed scrabbling at the sides cattle, for example, become so weak during droughts that they simply of the pit to escape. Modern mammals dig narrow holes to cannot haul themselves to their feet, and they die of exhaustion and reach water in dried-up river channels (e.g. Hamilton, 1985; hunger in a hollow produced partly by their weight and partly by Haynes, 1988; Emmons et al., 2004), but large mammals their feeble scrabbling. In some modern cases, the cattle had one or today tend to trample in great numbers around water holes, more feet trapped in the mud, but generally they did not. As preserved and enlarge the ponds (Butler, 1995, p. 95). Discrete pits are in fossil examples, one need not then expect to find a thick underlying not seen. Such widely trampled areas around waterholes layer of mud, and numerous animals might well be trapped on a single have been identified as an interpretation for certain mass dino- extensive horizon representing a single harsh summer. The absence of saur accumulations (Rogers, 1990), but there is no evidence for thick layers of mud or of evidence of trampling around the depressions such trampling at Kotel'nich. Further, although there is ample need not then speak against the general miring model. 78 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83

Miring has rarely been suggested for preservation of Permian ver- vertebrate fauna. Here, we use the term ‘microtopography’ to refer tebrates elsewhere. One example is a Diadectes skeleton, probably to the landscape-scale shape of the land surface, rather than the preserved upright in red mudstones of the Lower Permian Nocona plant-scale soil surface, as often used by ecologists (e.g. Beatty, 1984). Formation of West Texas, which Sander (1989) interpreted as mired The microtopography in the fine-grained fluviolacustrine settings and buried rapidly as an explanation for the posture and relative com- at Kotel'nich was generated in two ways (Fig. 16). First, the erosion pleteness of the specimen in comparison with the much more com- of a stable, mature palaeosol surface formed a series of shallow mon channel lag bonebeds nearby. Other examples from the scours. It seems most likely that the erosion was caused by a high- Permian are hard to identify, and the Kotel'nich deposit may be magnitude flood event. A common cause of high-magnitude flood unique for that time. events in floodplain settings is the abrupt shift (avulsion) of a drain- Miring has been proposed as the cause of death of many later age system into a low-lying area. Erosion of the Vanyushonki Member vertebrates, particularly dinosaurs and mammals (reviewed by Sander, palaeosol created a series of shallow scours that became sites for en- 1992 and Rogers and Kidwell, 2007), and the normal assumption has hanced rates of sedimentation and the mass burial of articulated par- been that these larger animals became stuck in the mud and could not eiasaur skeletons. It is uncertain if the flood event was responsible for extricate themselves. This is what is claimed for one of the closest taph- the mass death of the pareiasaurs, if a concentration of pareiasaur car- onomic equivalents to Kotel'nich, the Late Triassic Plateosaurus and casses had simply accumulated on the stable palaeosol surface prior Sellosaurus bonebeds in the Stubensandstein (=Löwenstein Forma- to flooding and erosion, or indeed, and this seems most likely, if the tion) and Knollenmergel (=Trossingen Formation) of SW Germany, animals were actually entering and dying in the hollows with no where numerous near-complete skeletons are preserved in upright physical transport. (belly-down) posture (Sander, 1992; Hungerbühler, 1996). These di- The second type of microtopography generated in the Kotel'nich nosaurs are preserved at the interface of fluvial sands overlain by succession is above thin, erosionally based sandstones, and these finer grained floodplain deposits, and presumably became stuck in the probably represent lows formed above abandoned or cut-off river wet sand. There is no hint that any of the skeletons of Plateosaurus channels. In some cases, these abandoned channels formed floodplain stood in hollows in the underlying sediment, nor was there a palaeosol. lakes, which ponded water and allowed the accumulation of laminat- Further, there is abundant evidence for scavenging in the form of asso- ed grey lacustrine sediments, plant remains, and fishes. Fragmentary ciated teeth of predators, and disarticulation and removal of certain remains are seen in the channel lags of the Chizhi and Sokol'ya Gora skeletal parts. A third difference is that the Plateosaurus skeletons members, and these probably represent weathered and disarticulated occur at several different stratigraphic levels, so the mode of death, if skeletal elements that entered the channel deposits by processes of it were miring possibly associated with aridification, must have hap- scour and bank erosion and they may have been transported consid- pened repeatedly. The fourth difference is that the Plateosaurus were erable distances from the site of death. much larger, weighing more than 2 tonnes, and so Sander (1992, p. 291) could argue that the adults perhaps became stuck and could not 8. Discussion and conclusion escape, despite strenuous efforts, whereas the smaller juveniles could escape and so were not preserved. Finally, the Plateosaurus skeletons Complete skeletons of terrestrial tetrapods may be preserved in are disarticulated and scattered in parts, suggesting some long period many settings, ranging from sand bars in the middle of rivers, over- of exposure after death. bank deposits, burrows, offshore marine sites, ash falls, and mummi- In all these five points, the Kotel'nich pareiasaurs differ: (1) the fied beneath aeolian dunes. Behrensmeyer (1988) distinguished two carcasses stand in hollows on top of a palaeosol; (2) they have not modes of vertebrate preservation in fluvial channels, the channel- been much scavenged; (3) they occur all at one stratigraphic level, lag and channel-fill modes. Channel-lag bones are preserved in the suggesting a single killing event; (4) the pareiasaurs are perhaps lower part of erosional channels, generally associated with pebbles not so massive, weighing perhaps 50–100 kg, that they could readily and intraclasts, often immediately above an erosive contact with become trapped in the mud in normal health; and (5) the skeletons finer-grained sediments below. Bones and teeth are generally heavily show almost no evidence of disarticulation, and so were buried quick- disarticulated, abraded, and concentrated in scours. This is the mode ly or at least without disturbance. of preservation of bones and other fossils in the Chizhi, and especially In another dinosaurian example, Varricchio et al. (2008) described the Sokol'ya Gora members. Channel-fill bones may be preserved in a small herd of juvenile and subadult ornithomimids trapped in a fine or coarse clastic sediments that fill a channel after it has been mud unit in the Upper Cretaceous of Mongolia. The carcasses were abandoned by active flow, and the bones tend to be less transported all belly-down, but scattered, and somewhat overlapping, on a single than in channel-lag examples, and sometimes carcasses may be bedding plane, somewhat aligned, and associated with isolated more or less complete. U-shaped channels and lenses indicate aban- bones. These were interpreted as having died in a drying lake or doned channels, and a fill of fine-grained sediment suggests sudden pond. An even more unusual dinosaurian example from the Jurassic abandonment and either a drastic reduction in the energy needed to Shishugou Formation of Xinjiang, China consists of numerous small transport coarser sediment or a barrier (e.g. vegetation) to the supply theropods apparently trapped in viscous mud within deep sauropod of sediment (Bridge, 1985; Behrensmeyer, 1988). This may be the footprints (Eberth et al., 2010). mode of preservation of the dicynodont skeletons at Port Kotel'nich. Eberth et al. (2010) note that most reported examples of miring Skeletons preserved in fluviatile settings are generally assumed to make the assumption that the animals became trapped in viscous have been transported some distance, as noted by Behrensmeyer, and mud and could not free themselves. In particular, they report that at- the channel-lag preservation mode is most familiar. Less well under- tempts by the animals to free themselves can increase the stickiness stood are her channel-fill deposits, where skeletons appear to be of the mud, and so make their efforts to escape even harder. As nearly or completely undamaged, and so presumably minimally noted, the Kotel'nich pareisaurs show no evidence for such viscous transported. Since 1988, several examples of such preservation have mud trapping the feet been noted among Permo-Triassic tetrapods (Smith, 1993; Smith and Swart, 2002) and dinosaurs (Rogers and Kidwell, 2000; 7.6. Landscape microtopography and the preservation of skeletons Therrien and Fastovsky, 2000; Ryan et al., 2001; Straight and Eberth, 2002; Rogers, 2005; González Riga and Astini, 2007). The channel- The Kotel'nich outcrops show the importance of microtopography fill deposition mode is often associated with major erosive surfaces of the landscape in providing taphonomic windows that locally in- below, and so has figured in debates about the significance of such crease vertical sedimentation rate and allow preservation of the levels in terms of omitted time and major sequence stratigraphic M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 79

Fig. 16. Block models showing the two main modes of exceptional vertebrate preservation in fluviolacustrine deposits at Kotel'nich (Type 1), in floodplain scours in the Vanyushonki Member, and in channel cutoffs in the ?Shestakovy Member at Port Kotel'nich, and the channel lags of the Chizhi and Sokol'ya Gora members (Type 2). marker horizons, whether they do (Straight and Eberth, 2002)ordo remains could accumulate, alternating with periods of relatively not (Rogers and Kidwell, 2000) coincide with major stillstands and rapid deposition that would bury bone-rich horizons, and (5) low scour surfaces that delimit sedimentary packets. Behrensmeyer rates of destruction by soil organisms and chemical dissolution be- (1988) outlined four categories of channel fill, A–D, representing cause of the combined effects of rapid burial and (perhaps) anaerobic fine to coarse sediment fills and increasing energy and speed of chan- conditions. nel fill; she observed categories B–D in the Pliocene of the Siwaliks, Fine-grained fluviolacustrine depositional environments in sub- and A–D in the Lower Permian of Texas. Her category-A channel siding sedimentary basins typically have exceptionally low surface re- fills, indicating the finest grain sizes and the slowest rate of channel lief and sediments are dispersed as thin sheets across large areas. filling, are likely to preserve the finest and least damaged vertebrate Rates of vertical sediment aggradation are typically slow and punctu- skeletons. Independent channels, as opposed to sheet sands, suggest ated by frequent episodes of non-deposition, weathering and soil for- high rates of subsidence. mation. This style of sedimentation has considerable implications for Behrensmeyer (1988) noted that bones in channel-fill deposits the vertebrate fossil record of fluviolacustrine deposits because back- were preserved in mixed to fine-grained deposits that filled channels ground sedimentation rates will generally be insufficient to conceal after they had been abandoned by sustained, active flow. Such de- large skeletal remains before they are destroyed by physical weather- posits usually occur in middle to later parts of channel fills, but occa- ing and scavenging. To achieve long-term preservation local condi- sionally, as here in the Vanyushonki Member, occur immediately tions must be developed that rapidly remove vertebrate skeletons above the basal eroded surface. Bones may be preserved in a variety from the zone of subaerial destruction. of modes, but complete and undamaged skeletons are commoner in At Kotel'nich, the succession is mostly fine-grained and deposited channel fills than in channel lags. The channels are abandoned and in laterally extensive, shallow lacustrine and floodplain environments have sporadic, waning flow with minor reworking of banks and bed- that aggraded slowly and were continuously modified by syndeposi- load sediments. Bones and skeletons in channel fills are either at the tional soil-forming processes that were generally not conducive to site of death or transported short distances; most are autochthonous the preservation of large vertebrate skeletons. Only at one level, on with respect to the local channel. top of a palaeosol that corresponds to a time of non-deposition, Behrensmeyer (1988) noted five correlates of the preservation of were hollows formed by water erosion or by animal activity, and an bones and skeletons in fluvial channels: (1) topographic lows likely episode of unusual aridity caused mass deaths of the dominant herbi- to receive and protect organic remains, (2) concentrations of animals vores, the pareiasaurs, as they feebly searched for food and water. near abandoned channels due to localised availability of food and They entered pre-existing hollows, or created those hollows, in water, particularly during times of restricted resources on the alluvial search of sustenance, and lacked the strength to escape, dying on plain, (3) localised transport, sorting, and hydraulic concentration of the spot, and generally showing little evidence of scavenging, perhaps bones, such as might occur during sporadic floods, (4) sedimentation because flesh-eating tetrapods had also died or had left the basin. Fol- patterns characterised by periods of non-deposition when attritional lowing the mass death, the carcasses became entombed under 80 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 subsequent fine-grained sediments deposited under water, but with- unexposed older parts of the succession, perhaps dating back to the Urz- out lateral currents that would have disturbed the carcasses. humian, as detected in the Kotel'nich borehole (Ignat'ev, 1962; Goman'kov, 1997) are not further considered here. Acknowledgements In his detailed biostratigraphic work, Golubev (2000, pp. 117–120) assigned primacy to the tetrapod-based biostratigraphic scheme. We are grateful to all members of the field crew when we worked Russian palaeontologists have always recognised two stratigraphic at Kotel'nich in summer 2009. This work was supported by NERC units in the Kotel'nich succession, an upper unit represented by the grant NE/C518973/1, and other costs were covered by our institu- Sokol'ya Gora Member, and a lower unit comprising the four members tions. A.J.N. publishes with the permission of the director of the Brit- beneath. The finds of the chroniosuchid Chroniosaurus levis, the batra- ish Geological Survey. We thank two anonymous reviewers for their chomorph Dvinosaurus primus,thepareiasaurProelginia cf. permiana very helpful advice. Key Russian-language papers about Kotel'nich (=Scutosaurus karpinskii), and the biarmosuchian theriodont Proburne- are available in English translation at http://palaeo.gly.bris.ac.uk/ tia viatkensis in the sandstone lens of the Sokol'ya Gora Member at Aga- Russia/kotelnich.html. fonovo and Sokol'ya Gora indicate assignment to the Il'inskoye Subcomplex, the middle division of the Sokolki Tetrapod Complex Appendix 1. Dating the Kotel'nich fossil assemblage (Fig. 6). The other tetrapod finds, listed earlier, from Port Kotel'nich and from the localities south of Kotel'nich on the Vyatka River, from The Russian stratigraphic system for the Permo-Triassic red beds the Vanyushonki, Shestakovy, and Chizhi members respectively (Golu- has been developed over the past hundred years as a result of exten- bev's beds 1, 6, and 5), are integral to, and type exemplars of, the sive fieldwork and comparative study. The closest ‘standard’ section Kotel'nich Subcomplex, the lowest division of the Sokolki Complex for comparison to Kotel'nich is the classic Sukhona River succession, (Fig. 6). some 275 km to the NNW, in the Dvina-Sukhona basin, Vologda Prov- In comparison with the standard Sukhona River sections, the key ince (Goman'kov, 1997; Golubev, 2000), and this was identified as biostratigraphic indicators, according to Golubev (2000, p. 119), are part of an extensive campaign since the 1960s to map throughout the chroniosuchids, basal tetrapods (=‘amphibians’) that were wide- the basins west and south of the Ural Mountains, including the Vyat- spread throughout Russia from the late Middle Permian to the Middle ka, Sukhona, and Dvina river basins (Fig. 1). In each basin, svitas Triassic. In the Sukhona River sections, Chroniosaurus levis is known (≈formations, although used as chronostratigraphic, not lithostrati- from the top of the Kichugskaya Packet (Mutovina and Mar'yushkina graphic, units) have been named, and these are sometimes further Sluda-C localities), while C. donguesensis is found some 20 m lower subdivided into ‘packets’ (≈members). Sections are correlated by (lower part of the Purtovinskaya Packet, Mikulino locality). Golubev means of mapping, magnetostratigraphy, and biostratigraphy (paly- (2000, p. 119) argues that the C. levis from Sokol'ya Gora is interme- nomorphs, ostracods, fishes, tetrapods). The stratigraphic scheme diate in terms of evolution between the Mikulinskaya and Mutovina (Fig. 6) is organised according to gorizonts, biozones defined on the chroniosuchids. Remains of chroniosuchids like those from Sokol'ya basis of key fossil groups. Gora are found on the Sukhona at the top of the Purtovinskaya or at The key relevant divisions are those of the Tatarian Stage, formerly the bottom of the Kichugskaya packets, indicating possible equiva- the last stratigraphic unit of the standard international time scale, but lence with the Sokol'ya Gora Member of the Kotel'nich section now replaced by the Chinese marine standard. Russian stratigraphers (Fig. 6). Thus, based on data from tetrapod fossils, the Kotel'nich sec- subdivide the Tatarian into three, the Urzhumian, Severodvinian, tion is correlated with the middle part of the Poldarsskaya Svita (Stre- and Vyatkian substages (Fig. 6), and magnetostratigraphic work lenskaya to Purtovinskaya packets) in the standard Sukhona River (Molostovskiy et al., 1979; Molostovskiy, 2005; Khramov et al., section, as noted by Golubev (in Newell et al., 2010, Fig. 2). 2006; Steiner, 2006; Taylor et al., 2009) has shown that the Tatarian Additional age data for correlation within the Russian system is much longer than formerly assumed (3–4 Myr), spanning in fact comes from the fishes and plants in the Chizhi Member plant- 14–15 Myr of the upper Middle Permian and all of the Late Permian, bearing lens. Goman'kov (1996, 1997) identified the macroplant as- equivalent to the Capitanian, Wuchiapingian, and Changhsingian semblage from the Chizhi Member as of ‘typical upper Tatarian ap- international stages. pearance’, whereas the pollen spectrum appears ‘archaic’, and dates The Kotel'nich succession has always been dated as late Tatarian, but this unit at least as older than Vyatkian, and places it just below the not terminal Tatarian, because it is overlain by the late Permian age of the plant-bearing deposits at Isady on the Sukhona River, Sokolki and Vyazniki tetrapod complexes, and its span is within the assigned to the Purtovinskaya Svita (Fig. 6). This is confirmed by pol- Severodvinian (Fig. 6). There has been a difference in interpretation of len associated with the plants in the Chizhi Member, which indicate the total time span represented at Kotel'nich, with the geological maps assignment to the rather broad palynocomplex (PK) 5 Vesicaspora– indicating that the Vanyushonki, Boroviki, and Chizhi members are Vitreisporites (Shelekhova, 1995), equivalent to the Vitreisporites parts of the P2jur (=Yurpalovskaya) beds, the Shestakovy Member cor- pallidus–Protohaploxypinus dvinensis Palynocomplex (Yaroshenko and responds to the P2pt (=Putyatinskaya) beds, and the Sokol'ya Gora Goman'kov, 1998). In Goman'kov's (1997) view then the plant- Member to the P2bk (=Bykovskaya) beds, as shown on USSR State bearing Chizhi Member of the Kotel'nich succession is dated to the Geological Map (1990): sheet number O-39-XIII (1:200,000) (Fridman, Yurpalovskaya Svita, roughly equivalent to the Isadskaya Svita on 1990; Goman'kov, 1997). The Yurpalovskaya and Putyatinskaya svitas the Sukhona River (Fig. 6). were named by Ignat'ev (1962) and Forsch (1963) in the Vyatka Basin, The fishes indicate an early Tatarian placement of the bed, but the including the Kotel'nich area (Fridman, 1990; Gusev, 1998; Goman'kov, ichthyocomplex (Fig. 6) cannot be determined exactly. Platysomus 2001). Coffa (1999), on the other hand, stated that the first four members biarmicus suggests the Platysomus Complex of the Ufimian, Kazanian, are components of the Yurpalovskaya Svita, and the Sokol'ya Gora Mem- and lower Tatarian, while Toyemia tverdochlebovae points to the over- ber is at the base of the overlying Putyatinskaya Svita. Finally, V. K. Golu- lying Toyemia Complex, characteristic of the upper Severodvinian. bev has suggested two correlations with the Sukhona section, first The occurrence of Amblypterina sp. suggests a more detailed assign- (Golubev, 2000, p. Fig. 35) equating the Kotel'nich succession with the ment, either to the Amblypterina costata Subcomplex, the uppermost Nyuksenitskaya to Purtovinskaya packets (Fig. 6), and then (Golubev, in of four subcomplexes in the Platysomus Complex, and characteristic Newell et al., 2010, Fig. 2) with the Strelenskaya to Kalikinskaya packets of the lower Tatarian, or the overlying Amblypterina pectinata Sub- (Fig. 6). These assignments indicate variously a short (Yurpalovskaya- complex, lowest of three subcomplexes in the Toyemia Complex and Putyatinskaya) or long (Yurpalovskaya-Bykovskaya) span for the matching the Il'inskian Tetrapod Complex (Esin, 1995; Esin and Kotel'nich succession (Fig. 6), and the differences must be resolved. The Mashin, 1998; Golubev, 2000). M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 81

References Fryberger, S.G., 1993. A review of aeolian bounding surfaces, with examples from the Permian Minnelusa Formation, USA. Geological Society, London, Special Publications Abdala, F., Cisneros, J.C., Smith, R.M.H., 2006. Faunal aggregation in the Early Triassic Karoo 73, 167–197. Basin: earliest evidence of shelter-sharing behavior among tetrapods? Palaios 21, Golubev, V.K., 1998. Revision of the Late Permian chroniosuchians (Amphibia, Anthra- 507–512. cosauromorpha) from Eastern Europe. Paleontological Journal 32, 390–401. Alonso-Zarza, A.M., 2003. Palaeoenvironmental significance of palustrine carbonates Golubev, V.K., 2000. Permian and Triassic chronosuchians and biostratigraphy of the and calcretes in the geological record. Earth-Science Reviews 60, 261–298. upper Tatarian deposits of Eastern Europe by tetrapods. Trudy Paleontologischeskogo Amalitzkiy, A.P., 1922. Diagnoses of the new forms of vertebrates and plants from the Instituta 276, 1–176 in Russian. Upper Permian on the North Dvina. Izvestiya Akademii Nauk SSSR, VI Seriya 16, Goman'kov, A.V., 1996. Palynological and floristic characteristics of the Tatarian Stage. 329–340 in Russian. Stratotipy i Opornye Razrezy Verkhnei Permi Povolzh'ya i Prikam'ya. Ekotsentr, Anderson, J.M., Cruickshank, A.R.I., 1978. The biostratigraphy of the Permian and Kazan, pp. 365–380. Triassic. A review of the classification and distribution of Permo-Triassic tetrapods. Goman'kov, A.V., 1997. The Permian (Tatarian) flora from the Kotel'nich vertebrate Palaeontologia Africana 21, 15–44. locality (Kirov region). Stratigrafiya, Geologicheskaya Korrelyatsiya 5 (4), 3–12 Beatty, S.W., 1984. Influence of microtopography and canopy species on spatial patterns in Russian. of forest understory plants. Ecology 65, 1406–1419. Goman'kov, A.V., 2001. The Type Section of the Tatarian Stage on the Vyatka River. Behrensmeyer, A.K., 1988. Vertebrate preservation in fluvial channels. Palaeogeography, Geos, Moscow. 112 pp. Palaeoclimatology, Palaeoecology 63, 183–199. González Riga, B.J., Astini, R.A., 2007. Preservation of large titanosaur sauropods in Benton, M.J., 1983. Dinosaur success in the Triassic: a noncompetitive ecological model. overbank fluvial facies: a case study in the Cretaceous of Argentina. Journal of The Quarterly Review of Biology 58, 29–55. South American Earth Sciences 23, 290–303. Benton, M.J., 2012. No gap in the Middle Permian record of terrestrial vertebrates. Gorsky, V.P., Gusseva, E.A., Crasquin-Soleau, S., Broutin, J., 2003. Stratigraphic data of Geology, 40. the Middle–Late Permian on Russian Platform. Geobios 36, 533–558. Benton, M.J., Walker, A.D., 1985. Palaeoecology, taphonomy and dating of Permo-Triassic Gradstein, F.M., Ogg, J.G., Smith, A.G. (Eds.), 2004. A Geologic Time Scale. Cambridge reptiles from Elgin, north-east Scotland. Palaeontology 28, 207–234. University Press, Cambridge. 589 pp. Benton, M.J., Tverdokhlebov, V.P., Surkov, M.V., 2004. Ecosystem remodelling Groenewald, G.H., Welman, J., Maceachern, J.A., 2001. Vertebrate burrow complexes among vertebrates at the Permian–Triassic boundary in Russia. Nature 432, from the Early Triassic Cynognathus Zone (Driekoppen Formation, Beaufort 97–100. Group) of the Karoo Basin, South Africa. Palaios 16, 148–160. Bordy, E.M., Sztanó, O., Rubidge, B.S., Bumby, A., 2011. Early Triassic vertebrate burrows Grunt, T.A. (Ed.), 2006. Late Permian of the Kanin Peninsula. Nauka, Moscow in from the Katberg Formation of the south-western Karoo Basin, South Africa. Russian. Lethaia 44, 33–45. Gusev, A.K., 1998. Reference section of the Tatarian Stage along the Vyatka River. In: Bridge, J.S., 1985. Paleochannel patterns inferred from alluvial deposits: a critical Esaulova, N.K., Lozovskiy, V.R., Rozanov, A.Yu. (Eds.), Stratotypes and Reference evaluation. Journal of Sedimentary Petrology 55, 579–589. Sections of the Upper Permian in the Regions of the Volga and Kama Rivers. Geos, Burov, B.V., Nurgaliev, D.K., and Heller, F.,1996.Theproblemsofpaleomagnetic Moscow, pp. 79–115. correlation of the Upper Permian deposits of the stratotype and marine for- Gubin, Yu.M., 1989. Some features of burial of pareiasaurs at the Upper Permian local- mations of Tethys. In: Shevelev, A.I. (Ed.), Permskie Otlozheniya Respubliki ity Kotel’nich. Voprosy Gerpetologii 7, 70–71, in Russian. Tatarstan. Ekotsentr, Kazan’, pp. 93–96 in Russian. Gubin, Yu.M., Golubev, V.K., Bulanov, V.V., Petuchov, S.V., 2003. Pareiasaurian tracks Butler, D.J., 1995. Zoogeomorphology: Animals as Geomorphic Agents. Cambridge: from the Upper Permian of Eastern Europe. Paleontological Journal 37, 514–523. Cambridge University Press, Cambridge. 233 pp. Hamilton III, W.J., 1985. Demographic consequences of a food and water shortage to desert Coffa, A.A., 1997. Stratigraphy and correlation of the continental red bed sequence at Chacma baboons, Papio ursinus. International Journal of Primatology 6, 451–462. the Kotel'nich Upper Permian fossil tetrapod locality, Russia. Geological Society Hartmann-Weinberg, A.P., 1933. Die Evolution der Pareiasauriden. Trudy Paleontologi- of Australia, Abstracts 46 (15), 17. cheskogo Instituta AN SSSR 3, 3–66. Coffa, A.A., 1998. Aeolian vs. fluvial origin for the Boroviki Member, Kotel'nich Upper Hartmann-Weinberg, A.P., 1937. Pareiasauriden als Leitfossilien. Problemy Paleontologii Permian fossil tetrapod localities, Vyatka Basin, Russia. Geological Society of Australia, 2, 649–712. Abstracts 52, 7. Haynes, G., 1988. Mass deaths and serial predation: comparative taphonomic studies Coffa, A.A., 1999. Sedimentology, stratigraphy and correlation of the continental red bed of modern large mammal death sites. Journal of Archeological Science 15, sequence at the Kotel'nich Late Permian fossil tetrapod localities, Russia. Proceedings 219–235. of International Symposium “Upper Permian Stratotypes of the Volga Region”.Geos, Hungerbühler, A., 1996. Taphonomy of the prosauropod dinosaur Sellosaurus, and its Moscow, pp. 77–86. implications for carnivore faunas and feeding habits in the Late Triassic. Palaeogeo- Damiani, R., Modesto, S.P., Yates, A., Neveling, J., 2003. Earliest evidence of cynodont graphy, Palaeoclimatology, Palaeoecology 143, 1–29. burrowing. Proceedings of the Royal Society, Series B 270, 1747–1751. Ignat'ev, V.I., 1962. Tatarian Stage of Central and Eastern Regions of the Russian Platform. Eberth, D.A., Shannon, M., Noland, B.G., 2007. A bonebeds database: classification, Part I: Stratigraphy. Izdatel'stvo Kazanskogo Universiteta, Kazan. 334 pp. biases, and patterns of occurrence. In: Rogers, R.R., Eberth, D.A., Fiorillo, A.R. (Eds.), Ignat'ev, V.I., 1963. Tatarian Stage of Central and Eastern Regions of the Russian Bobebeds: Genesis, Analysis, and Paleobiological Significance. University of Chicago Platform. Part II: Facies, Palaeogeography. Izdatel'stvo Kazanskogo Universiteta, Press, pp. 103–219. Kazan. 338 pp. Eberth, D.A., Xu, X., Clark, J.M., 2010. Dinosaur death pits from the Jurassic of China. Ivakhnenko, M.F., 1987. The Permian parareptiles of the USSR. Trudy Paleontologiches- Palaios 25, 112–125. kogo Instituta AN SSSR 223, 1–160 in Russian. Efremov, I.A., 1937. On stratigraphic division of the continental Permian and Triassic of Ivakhnenko, M.F., 1992. The Late Permian faunistic assemblages of tetrapods from the S.S.S.R. from the fauna of terrestrial vertebrates. Doklady Akademii Nauk SSSR Eastern Europe and their South Gondwanan analogues. Paleontologiya i Stratigrafiya 16, 125–132 in Russian. Kontinental'nikh Otlogenii Permi i Triasa Severnoy Evrazii. Paleontologicheskii Efremov, I.A., 1940. Preliminary description of new Permian and Triassic tetrapods Institut RAN, Moscow, pp. 6–7. in Russian. from the USSR. Trudy Paleontologicheskiy Instituta SSSR 10(2), 1–140, in Russian. Ivakhnenko, M.F., 1994. A new Late Permian dromasaurian (Anomodontia) from Eastern Efremov, I.A., 1939. On the evolution of Permian faunas of Tetrapoda of the USSR and Europe. Paleontological Journal 28, 96–103. on divisions of the continental Permian into stratigraphic zones. Izvestiya Akade- Ivakhnenko, M.F., 1997. New Late Permian nycteroleterids from Eastern Europe. mii Nauk SSSR, Seriya Biologiya 2, 272–289, in Russian. Paleontological Journal 31, 552–558. Efremov, I.A., 1941. Short survey of faunas of Permian and Triassic Tetrapoda of the Kashtanov, S.G., 1934. On the discovery of Permian reptiles on the River. Vyatka, near USSR. Sovetskaya Geologiya 5, 96–103 in Russian. the town of Kotel’nich. Priroda 1934 (2), 74–75, in Russian. Efremov, I.A., V’yushkov, B.P., 1955. Catalogue of localities of Permian and Triassic ter- Khlyupin, A.Yu., 2007. Cemetery of the Permian reptiles. Paleomir 1, 50–57. restrial vertebrates in the territories of the U.S.S.R. Trudy Paleontologicheskiy Insti- Khlyupin, A.Yu, Coffa, A.A., Lalomov, A.V., Naugol'nykh, S.V., 2000. Permian Park on the tuta 46, 1–185, in Russian. Vyatka Soil. Kotel'nich Paleontological Museum. 55 pp. [In Russian.]. Emmons, L.H., Flores, R.P., Alpirre, S.A., Swarner, M.J., 2004. Bathing behavior of Giant Khramov, A.N., 1963. Palaeomagnetic investigations of Upper Permian and Lower Triassic anteaters (Myrmecophaga tridactyla). Edentata 6, 41–43. sections on the northern and eastern Russian Platform. Trudy VNIGRI 204, 145–174 in ESIN, D.N. 1995. Latest Permian Palaeoniscids from the European Parts of Russia.Candidate Russian. Dissertation, Geological and Mineralogical Science, Moscow, 23 [in Russian]. Khramov, A.N., Kommissarova, R.A., Iosifidi, A.G., Popov, V.V., Bazhenov, M.L., 2006. Esin, D.N., Mashin, V.L., 1998. Ichthyolites. In: Esaulova, N.K., Lozovskiy, V.R., Rozanov, Upper Tatarian magnetostratigraphy of the Sukhona River sequence: a re-study, A.Yu. (Eds.), Stratotypes and Reference Sections of the Upper Permian in the Regions available online at http://geo.phys.spbu.ru/geocosm2006/proc_contents.shtml. of the Volga and Kama Rivers. Ekotsentr, Kazan, pp. 176–188. Kordikova, E.G., Khlyupin, A.Yu, 2001. First evidence of a neonate dentition in pareiasaurs Forsch, N.N., 1963. On the stratigraphic division and correlation of Tatarian sec- from the Upper Permian of Russia. Acta Palaeontologica Polonica 46, 589–594. tions of the east of the Russian platform from a set of lithologo-stratigraphic, Krassilov, V.A., Karasev, E., 2009. Paleofloristic evidence of climate change near and beyond palaeomagnetic & palaeontological data. Trudy VNIGRI 204, 175–211 in the Permian–Triassic boundary. Palaeogeography, Palaeoclimatology, Palaeoecology Russian. 284, 326–336. doi:10.1016/j.palaeo.2009.10.012. Fridman, B.I. 1990. State Geological Map of the Russian Federation, Scale 1:200,000, Kraus, M.J., Middleton, L.T., 1987. Dissected paleotopography and base-level changes in Upper Volga Series, Sheets O-38-XVIII (Svecha), O-39-XIII (Kotel’nich), Explanato- a Triassic fluvial sequence. Geology 15, 18–21. ry Memoir. Izdatel’stvo Sankt-Peterburgskoi Geograficheskoi Fabriki VSEFGEI, Krotov, P.I., 1894. Geological map of European Russia. Sheet 89. Geological part. Orohy- Saint Petersburg, 114 pp., in Russian. drographic outline of the western parts of Vyatka Province within Sheet 89. Trudy Fröbisch, J., Reisz, R.R., 2009. The Late Permian herbivore Suminia and the early evolution Geologicheskogo Komiteta 13 (2), 1–228, in Russian. of arboreality in terrestrial vertebrate ecosystems. Proceedings of the Royal Society, Krotov, P.I., 1912. The western part of the Vyatka Province. Sheet 89. Trudy Geologi- Series B 276, 3611–3618. doi:10.1098/rspb.2009.0911. cheskogo Komiteta Novaya Seriya 64, 1–128 in Russian. 82 M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83

Kurkin, A.A., 2000. New dicynodonts from the Upper Permian of the Vyatka Basin. Sander, P.M., 1989. Early Permian depositional environments and pond bonebeds in Paleontological Journal 34, S203–S210. central Archer County, Texas. Palaeogeography, Palaeoclimatology, Palaeoecology Kurkin, A.A., 2011. Permian anomodonts: paleobiogeography and distribution of the 69, 1–21. group. Paleontological Journal 2011, 71–84. Sander, P.M., 1992. The Norian Plateosaurus bonebeds of central Europe and their Lee, M.S.Y., 2000. The Russian pareiasaurs. In: Benton, M.J., Shishkin, M.A., Unwin, D.M., taphonomy. Palaeogeography, Palaeoclimatology, Palaeoecology 93, 255–299. Kurochkin, E.N. (Eds.), The Age of Dinosaurs in Russia and Mongolia. Cambridge Shcherbakov, D.E., 2008. On Permian and Triassic insect faunas in relation to biogeography University Press, Cambridge, pp. 71–85. and the Permian–Triassic crisis. Paleontological Journal 42, 15–31. Loope, D.B., Dingus, L., Swisher III, C.C., Minjin, C., 2001. Life and death in a Late Cretaceous Shelekhova, M.N., 1995. Palynostratigraphy of the Tatarian Stage of the Russian plates. dune field, Nemegt basin, Mongolia. Geology 26, 27–30. Paleontologiya i Stratigrafiya Kontinental'nikh Otlogenii Permi i Triasa Severnoy Lozovskiy, V.R., Esaulova, N.K., 1998. Permian–Triassic Boundary in the Continental Evrazii. Paleontologicheskii Institut RAN, Moscow. 28 [in Russian]. Series of Eastern Europe. Geos, Moscow. 246 pp. [in Russian.]. Shishkin, M.A., Sennikov, A.G., Novikov, I.V., Ilyina, N.V., 2006. Differentiation of tetrapod Lozovskiy, V.R., Minikh, M.G., Grunt, T.A., Kukhtinov, D.A., Ponomarenko, A.G., Sukacheva, communities and some aspects of biotic events in the Early Triassic of Eastern Europe. I.D., 2009. The Ufimian Stage of the East European scale: status, validity, and correla- Paleontological Journal 40, 1–10. tion potential. Stratigraphy and Geological Correlation 17, 602–614. Smith, R.M.H., 1987. Helical burrow casts of therapsid origin from the Beaufort Group Lucas, S.G., 2004. A global hiatus in the Middle Permian tetrapod fossil record. Stratigraphy (Permian) of South Africa. Palaeogeography, Palaeoclimatology, Palaeoecology 1, 47–64. 60, 155–170. Lucas, S.G., 2006. In: Lucas, S.G., Cassinis, G., Schneider, J.W. (Eds.), Global Permian Smith, R.H.M., 1993. Vertebrate taphonomy of Late Permian floodplain deposits in the Tetrapod Biostratigraphy and Biochronology. Non-marine Permian Biostratigra- southwestern Karoo Basin of South Africa. Palaios 8, 45–67. phy and Biochronology: Special Publication, 265. Geological Society, London, Smith, R.H.M., Swart, R., 2002. Changing fluvial environments and vertebrate taphonomy in pp. 65–93. response to climatic drying in a Mid-Triassic rift valley fill: the Omingonde Formation Mack, G.H., James, W.C., Monger, H.C., 1993. Classification of paleosols. Geological Society (Karoo Supergroup) of Central Namibia. Palaios 17, 249–267. of America Bulletin 105, 129–136. Steiner, M.B., 2006. The magnetic polarity time scale across the Permian–Triassic Mellink, E., Martin, P.S., 2001. Mortality of cattle on a desert range: paleobiological boundary. In: Lucas, S.G., Cassinis, G., Schneider, J.W. (Eds.), Non-Marine Permian implications. Journal of Arid Environments 49, 671–675. Biostratigraphy and Biochronology. : Geological Society of London, Special Publications, Modesto, S., Botha-Brink, J., 2010. A burrow cast with Lystrosaurus skeletal remains 265. The Geological Society of London, London, pp. 15–38. from the Lower Triassic of South Africa. Palaios 25, 274–281. Straight, W.H., Eberth, D.A., 2002. Testing the utility of vertebrate remains in recognizing Modesto, S., Rybczynski, N., 2000. The amniote faunas of the Russian Permian: Implications patterns in fluvial deposits: an example from the Lower Horseshoe Canyon Formation, for Late Permian terrestrial vertebrate biogeography. In: Benton, M.J., Shishkin, M.A., Alberta. Palaios 17, 472–490. Unwin, D.M., Kurochkin, E.N. (Eds.), The Age of Dinosaurs in Russia and Mongolia. Sumida, S.S., 2001. A phylogenetic perspective on locomotory strategies in early amniotes. Cambridge University Press, Cambridge, pp. 17–34. American Zoologist 41, 586–597. Molostovskiy, E.A., 1983. Palaeomagnetic Stratigraphy of the Upper Permian and Triassic Sumin, D.L., 2009. Hibernation as a factor ensuring preservation of pareiasaurs at the of East European Parts of the S.S.S.R. Izdatel'stvo Saratovstkogo Universiteta, Saratov. Kotel'nich locality. In: Shishkin, M.A., Tverdokhlebov, V.P. (Eds.), Issledovaniya po 168 [in Russian]. paleontologii i biostratigrafii drevnikh kontinental'nikh otlogenii (Pamyati Professora Molostovskiy, E.A., 2005. Magnetostratigraphic correlation of Upper Permian marine and G. Ocheva). Izdatel'stvo “Nauchnaya Kniga”,Saratov,pp.171–174. in Russian. continental formations. Stratigrafiya Geologicheskaya Korrelyatsiya 13, 49–58 in Tatarinov, L.P., 1968. New theriodonts from the Upper Permian of the USSR. Upper Russian. Palaeozoic and Mesozoic Amphibians and Reptiles of the USSR. Nauka, Moscow, Molostovskiy, E.A., Molostovskaya, I.I., Minikh, A.V., 1979. Stratigraphy of the Tatarian pp. 32–45. Stage in the basin of the River Sukhona 1979 Izvestiya Vyzzhikh Uchebnykh Zavednii Tatarinov, L.P., 1995a. Viatkosuchus sumini — a new therocephalian from the Upper (Geologiya i Razvedka) (6), 31–38 in Russian. Permian of the Kirov Province. Palaeontological Journal 19, 84–97. Nalivkin, D.V., 1973. Geology of the U.S.S.R. Oliver and Boyd, Edinburgh. 855 pp. Tatarinov, L.P., 1995b. A new ictidosuchid Karenites ornamentatus (Theriodontia) from Newell, A.J., Tverdokhlebov, V.P., Benton, M.J., 1999. Interplay of tectonic and climate the Upper Permian of the Kotel'nich locality in the Kirov region. Russkii Zhurnal on a transverse fluvial system, Upper Permian, southern Uralian foreland basin. Gerpetologii 2 (1), 18–33. Sedimentary Geology 127, 11–29. Tatarinov, L.P., 1997. New scaloposaur (Reptilia, Theriodontia) with an unusual sensory Newell, A.J., Sennikov, A.G., Benton, M.J., Molostovskaya, I.I., Golubev, V.K., Minikh, A.V., system, from the Upper Permian of the Kirov Region. Paleontological Journal 31, Minikh, M.G., 2010. Disruption of playa-lacustrine depositional systems at the 655–661. Permo-Triassic boundary: evidence from Vyazniki and Gorokhovets on the Russian Tatarinov, L.P., 1999a. The first scaloposaurid (Reptilia, Theriodontia) from Russia Platform. Journal of the Geological Society of London 167, 695–716. doi:10.1144/ (Upper Permian, Kirov Region). Paleontological Journal 33, 278–288. 0016-76492009-103. Tatarinov, L.P., 1999b. New theriodonts (Reptilia) from the Late Permian fauna of the Nikishin, A.M., Ziegler, P.A., Stephenson, R.A., Cloetingh, S.A.P.L., Furne, A.V., Fokin, P.A., Kotel'nich locality, Kirov Region. Paleontological Journal 33, 550–556. Ershov, A.V., Bolotov, S.N., Korotaev, M.V., Alekseev, A.S., Gorbachev, V.I., Shipilov, Tatarinov, L.P., 2000. New material on scaloposaurians (Reptilia, Theriodontia) from E.V., Lankreijer, A., Bembinova, E.Y., Shalimov, I.V., 1996. Late Precambrian to the Upper Permian of the Kotel'nich Locality, Kirov Region. Paleontological Journal Triassic history of the East European Craton: dynamics of sedimentary basin 34, S187–S202. evolution. Tectonophysics 268, 23–63. Tatarinov, L.P., 2004a. A postcranial skeleton of the gorgonopsian Viatkogorgon Ochev, V.G., 1995. Mysterious Kotel'nich. Priroda 53–59 1995. ivachnenkoi (Reptilia, Theriodontia) from the Upper Permian Kotel'nich locality, Ochev, V.G., Surkov, M.V., 2000. The history of excavation of Permo-Triassic vertebrates Kirov Region. Paleontological Journal 38, 437–447. from Eastern Europe. In: Benton, M.J., Shishkin, M.A., Unwin, D.M., Kurochkin, E.N. Tatarinov, L.P., 2004b. The postcranial skeleton of the Late Permian scaloposaurian (Eds.), The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press, Karenites ornamentatus (Reptilia, Theriodontia) from the Kirov Region. Paleontological Cambridge, pp. 1–16. Journal 38, 548–555. Ogg, J.G., Ogg, G., Gradstein, F.M. (Eds.), 2008. The Concise Geologic Time Scale. Cambridge Taylor, G.K., Tucker, C., Twitchett, R.J., Kearsey, T., Benton, M.J., Newell, A.J., Surkov, University Press, Cambridge. 184 pp. M.V., Tverdokhlebov, V.P., 2009. Magnetostratigraphy of Permian/Triassic boundary Olson, E.C., 1962. Late Permian terrestrial vertebrates, U.S.A. and U.S.S.R. American sequences in the Cis-Urals, Russia: no evidence for a major temporal hiatus. Earth Philosophical Society Transactions, New Series 52, 1–224. and Planetary Science Letters 281, 36–47. Rogers, R.R., 1990. Taphonomy of three dinosaur bone beds in the Upper Cretaceous Therrien, F., Fastovsky, D.E., 2000. Paleoenvironments of early theropods, Chinle Formation Two Medicine Formation of Montana: evidence for drought-related mortality. (Late Triassic), Petrified Forest National Park, Arizona. Palaios 15, 194–211. Palaios 5, 394–413. Tikhvinskaya, E.I., 1946. Stratigraphy of Permian red beds of the eastern Russian Platform Rogers, R.R., 2005. Fine-grained debris flows and extraordinary vertebrate burials in (the 100th anniversary of the Permian System 1841–1941) Volume 1 Uchenye the Late Cretaceous of Madagascar. Geology 33, 297–300. doi:10.1130/G21036.1. Zapiski Kazan'skogo Universiteta 306 (4) Geologiya, 16, 354 pp. Rogers, R.R., Kidwell, S.M., 2000. Association and taphonomy of terrestrial vertebrate Tverdokhlebov, V.P., 2009. Facies-genetic analysis of Tatarian deposits and conditions of fossils with terrestrial discontinuity surfaces in Judith River Formation, Montana. formation of the ‘Koetl'nich’ locality. Verkhniy Paleozoi Rossii: Stratigraficheskiya i Journal of Geology 108, 131–154. Faunal'niyi Analiz, Kazan', 27–30 September 2009. Izdatel'stvo Kazan'skogo Rogers, R.R., Kidwell, S.M., 2007. A conceptual framework for the genesis and analysis Universiteta, pp. 1–3. in Russian. of vertebrate skeletal concentrations. In: Rogers, R.R., Eberth, D.A., Fiorillo, A.R. Tverdokhlebov, V.P., Shminke, L.N., 1990. Aeolian deposits of the Tatarian Stage in (Eds.), Bobebeds: Genesis, Analysis, and Paleobiological Significance. University the basin of the River Vyatka. Doklady Akademii Nauk SSSR 315, 934–936 in of Chicago Press, pp. 1–63. Russian. Rubidge,B.S.,Erwin,D.H.,Ramezani,J.,Bowring,S.A.,DeKlerk,W.J.,2010.Thefirst Tverdokhlebov, V.P., Tverdokhlebova, G.I., Surkov, M.V., Benton, M.J., 2003. Tetrapod radiometric dates for the Beaufort Group. Karoo Supergroup of South Africa. In: localities from the Triassic of the SE of European Russia. Earth-Science Reviews Mostovski,M.B.,Ovechkina,M.N.(Eds.), Proceedings of the 16th Conference 60, 1–66. of the Palaeontological Society of Southern Africa, Howick, August 5–8, 2010, Tverdokhlebov, V.P., Tverdokhlebova, G.I., Minikh, A.I., Surkov, M.V., Benton, M.J., 2005. pp. 82–83. Upper Permian vertebrates and their sedimentological context in the South Urals, Ryan, M.J., Russell, A.P., Eberth, D.A., Currie, P.J., 2001. The taphonomy of a Centrosaurus Russia. Earth-Science Reviews 69, 27–77. (Ornithischia: Ceratopsidae) bone bed from the Dinosaur Park Formation (Upper V'yushkov, B.P., 1953. Locality for pareiasaurs on the Vyatka below Kotel'nich. Byulleten' Campanian), Alberta, Canada, with comments on cranial ontogeny. Palaios 16, Moskovskogo Obshchestva Ispytatelei Prirody, Otdel Geologicheskii 28, 49–56 482–506. [in Russian]. Rybczinski, N., 2000. Cranial anatomy and phylogenetic position of the basal anomodont Varricchio, D.J., Sereno, P.C., Zhao, X., Tan, L., Wilson, J.A., Lyon, G.H., 2008. Mud-trapped (Therapsida), Suminia getmanovi. Zoological Journal of the Linnean Society 130, herd captures evidence of distinctive dinosaur sociality. Acta Palaeontologica Polonica 329–373. 53, 567–578. M.J. Benton et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 319-320 (2012) 58–83 83

Voigt, S., Hminna, A., Saber, H., Schneider, J.W., Klein, H., 2010. Tetrapod footprints from Yaroshenko, O., Goman'kov, A.V., 1998. Miospores. In: Lozovskiy, V., Esaulova, N.K. the uppermost level of the Permian Ikakern Formation (Argana Basin, Western High (Eds.), Granitsa Permi i Triasa v kontinental'nikh seryakh vostochnoy Evropy. Atlas, Morocco). Journal of African Earth Sciences 57, 470–478. Geos, Moscow, pp. 113–129. in Russian. Walling, D.E., He, Q., 1998. The spatial variability of overbank sedimentation on river Zharkov, M.A., Chumakov, N.M., 2001. Paleogeography and sedimentation settings floodplains. Geomorphology 24, 209–223. during Permian–Triassic reorganizations in biosphere. Stratigraphy and Geological Weigelt, J., 1989. Recent Vertebrate Carcasses and their Paleobiological Implications. Correlation 9, 340–363. University of Chicago Press, Chicago. 188 pp. Yakimenko, E.Yu., Inozemtsev, S.A., Naugolnykh, S.V., 2004. Upper Permian paleosols (Salarevskian Formation) in the central part of the Russian Platform: paleoecology and paleoenvironment. Revista Mexicana de Ciencias Geológicas 21, 110–119.